C++: Diff-informed queries: phase 3 (non-trivial locations)

[d10c]

This PR enables diff-informed mode on queries that select a location other than dataflow source or sink. This entails adding a non-trivial location override that returns the locations that are actually selected.

Prior work includes PRs like #19663, #19759, and #19817. This PR uses the same patch script as those PRs to find candidate queries to convert to diff-enabled. This is the final step in mass-enabling diff-informed queries on all the languages.

Commit-by-commit reviewing is recommended.

• I have split the commits that add/modify tests from the ones that enable/disable diff-informed queries.
• If the commit modifies a .qll file, in the commit message I've included links to the queries that depend on that .qll for easier reviewing.
• Feel free to delegate parts of the review to others who may be more specialized in certain languages.

Potentially tricky cases:

• [TEST] C++: CWE-020/ExternalAPI: add tests based on qlhelp: I wasn't able to get alerts to show up for the qhelp-based tests; can someone from the language team chip in to what a useful test would look like? Similar case with the Python TimingAttackAgainstHash test. In contrast, in [TEST] Java: CWE-020/ExternalAPI I was able to get alerts just from the qhelp example, and in [TEST] C++: CleartextSqliteDatabase I was able to get alerts from a mostly Copilot-written test.

[Copilot]

Pull Request Overview

This PR enables diff-informed mode on C++ security queries that select locations other than dataflow source or sink. The changes add location override predicates to allow these queries to work with diff-informed analysis, which is part of the final phase of mass-enabling diff-informed queries across all languages.

Key changes include:

• Addition of observeDiffInformedIncrementalMode() predicates to enable diff-informed mode
• Implementation of getASelectedSourceLocation() and getASelectedSinkLocation() predicates to specify relevant locations
• Creation of test files for CWE-020 (External API) and CWE-313 (Cleartext SQLite Database) queries

Reviewed Changes

Copilot reviewed 41 out of 43 changed files in this pull request and generated no comments.

File	Description
Multiple security query files	Added diff-informed mode configuration with location override predicates
CleartextSqliteDatabase test files	Added comprehensive test case with SQLite security vulnerabilities
ExternalAPI test files	Added test infrastructure for external API queries
ExternalAPIsSpecific.qll files	Disabled diff-informed mode for library code used by multiple queries