feat: Add Jmespath expression function in frontend

[TomasEng]

Important

This pull request is stacked upon #18982, which should be merged first.

Description

This pull request adds support for Jmespath queries in our expression language. This includes a new dependnecy; Jmespath JS.

This also includes a new function evaluator class; JmespathFunctionEvaluator. Since it follows the same pattern as ObjectFunctionEvaluator, I have also added an abstract class that both of them extend and moved them into a separate folder. In the future, we may consider refactoring more of the functions the same way in order to make expression-functions.ts easier to navigate.

Here is the corresponding implementation in backend: Altinn/app-lib-dotnet#1790

Verification

• Related issues: Add JMESPath expression app-frontend-react#4196
• Your code builds clean without any errors or warnings
• Manual testing done (required)
• Relevant automated test added (if you find this hard, leave it and we'll help out)

Summary by CodeRabbit

• New Features
  • Introduced JMESPath query expressions to the expression system. Users can now perform advanced data querying and transformation using standard JMESPath syntax, including filtering, projecting data across lists, selecting properties, and evaluating built-in functions on complex data structures.

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📝 Walkthrough

Walkthrough

This PR adds JMESPath expression function support to the expression evaluator system. It introduces a base evaluator class for standardised error handling, implements a JMESPath-specific evaluator, defines the schema contract, integrates the new function into the expression registry, refactors an existing evaluator to use the new base class, and includes comprehensive test fixtures.

Changes

JMESPath Expression Function Implementation

Layer / File(s)	Summary
Validation and base evaluator infrastructure src/App/frontend/src/features/expressions/validation.ts, src/App/frontend/src/features/expressions/function-evaluators/FunctionEvaluator.ts	Adds assertValidValue() assertion helper to enforce runtime validation of expression values, and introduces abstract FunctionEvaluator<Arguments, ReturnValue> base class that centralises evaluation context, argument storage, and exception handling via throwRuntimeException() method.
Validation assertion tests src/App/frontend/src/features/expressions/validation.test.ts	Test suite for assertValidValue covering rejection of invalid types (BigInt) and acceptance of valid values (numbers and other primitives).
Expression schema definition src/App/frontend/schemas/json/layout/expression.schema.v1.json	Adds func-jmespath JSON schema definition specifying the array-form expression ["jmespath", <data>, <query>] with exactly two parameters, and registers it in the definitions.any.anyOf union to enable schema validation.
JMESPath evaluator implementation src/App/frontend/package.json, src/App/frontend/src/features/expressions/function-evaluators/JmespathFunctionEvaluator.ts	Adds jmespath v0.16.0 runtime dependency and implements JmespathFunctionEvaluator that executes JMESPath queries via jmespath.search(), validates results with assertValidValue, and propagates errors using the base class exception mechanism with type checking for the query parameter.
Expression function registration and wiring src/App/frontend/src/features/expressions/expression-functions.ts	Registers the jmespath function in ExprFunctionDefinitions with (Any, String) parameters and Any return type, updates imports to reference JmespathFunctionEvaluator, and implements the runtime instantiation in ExprFunctionImplementations.
ObjectFunctionEvaluator base class migration src/App/frontend/src/features/expressions/function-evaluators/ObjectFunctionEvaluator.ts	Refactors ObjectFunctionEvaluator to extend FunctionEvaluator<ValidValue[], ValidObject> base class, replacing private field storage with protected getters, and replacing direct ExprRuntimeError construction with throwRuntimeException() helper calls whilst preserving key validation and even/odd argument filtering logic.
JMESPath test fixture src/App/frontend/src/features/expressions/shared-tests/functions/jmespath/jmespath.json	Comprehensive test fixture covering JMESPath operations: property selection, object and list returns, list projections, filtering, literal expressions, built-in functions (abs), and error cases validating expected exception messages for invalid queries, missing arguments, and type mismatches.

Sequence Diagram

sequenceDiagram
  participant ExprFunction as Expression Function
  participant Evaluator as JmespathFunctionEvaluator
  participant JMESPath as jmespath.search()
  participant Validation as assertValidValue
  ExprFunction->>Evaluator: new(context, [data, query])
  Evaluator->>JMESPath: search(data, query)
  JMESPath-->>Evaluator: result
  Evaluator->>Validation: assertValidValue(result)
  Validation-->>Evaluator: validated
  Evaluator-->>ExprFunction: return ValidValue

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Suggested labels

frontend, squad/data

Suggested reviewers

• ivarne
• olavsorl

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🐰 A query language hops into the system,
JMESPath expressions now we can list 'em,
Base classes shared, no more duplication,
Validation firm, safe computation! ✨

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: adding JMESPath expression function support to the frontend.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description check	✅ Passed	The pull request description adequately covers the changes, includes relevant context about dependencies and architectural decisions, and verifies all required checklist items.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch add-jmespath-function

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