Compile lifted user-defined AndAlso and OrElse operators - #597

Compile valid AndAlso/OrElse expressions over nullable structs with user-defined logical operators, which currently fail strict FEC compilation.

Use one TryEmitUserDefinedLogicalOperator helper for both lifted and non-lifted custom operators. Share left operand storage, op_False/op_True testing, right operand evaluation on an empty stack, the selected bitwise method call, short-circuit branches, and result merging. Keep nullable checks, unwrapping, wrapping, and null-result labels conditional on lifting. Existing method lookup and operand contexts are preserved for each path; ordinary Boolean emission remains separate.

Strict Standard/LightExpression tests cover:

• Lifted values and nulls, short-circuit traces, explicit methods, ignored results, right-side finally cleanup, and direct factories, compared with System.Linq.Expressions.
• Non-lifted reference identity and operator call counts, struct operators, explicit methods, ignored-result effects, and right operands containing try/catch.

Validation

Current master base: 76f2b28f9363d3364be75dc9830c7e303aea8b3a. Release solution build: zero warnings/errors. Both APIs have strict regression coverage with fallback disabled.

Shared-helper measurements

Compare separate emitters (1bac8a3b) with the shared helper (394f8e85), both built on the master base above. Both configurations support the measured lifted expressions; these are direct before/after measurements of helper unification. Master itself does not successfully compile those lifted trees.

Windows ARM64, .NET 8.0.28 and 10.0.9, Release, tiering disabled. Prebuilt trees, Light conversion outside timing, isolated load contexts, one CPU, nine alternating samples per phase, and two fresh process rounds in opposite load order with approximately 100 ms pair calibration. Compilation and invocation are measured separately. Timings combine the 18 samples; allocation counts use thread allocation counters.

Every measured case retains identical emitted IL and unchanged compilation allocations. All measured invocations allocate zero. The measurements cover non-lifted struct/reference operators, lifted value/null paths, AndAlso/OrElse and a Boolean control. CPU timings vary between rounds; slower observations are retained below, and no exact timing-neutrality or speedup claim is made.