Do not report MA0173 when the value cannot be captured by a lambda

[meziantou]

Problem

The MA0173 code fix rewrites Interlocked.CompareExchange(ref field, value, null) into LazyInitializer.EnsureInitialized(ref field, () => value). It wraps the value expression in a lambda without checking that the expression can legally live inside one, so it can turn compiling code into code that does not compile:

using System.Threading;
public class Sample
{
    static object target;
    public static void Run(ref int value)
    {
        Interlocked.CompareExchange(ref target, new System.Text.StringBuilder(value), null);
    }
}

The fixed code fails with CS1628, as a lambda cannot capture the ref parameter value.

Change

UseLazyInitializerEnsureInitializeAnalyzer now walks the value operation before reporting and skips the diagnostic when any descendant is something a lambda cannot capture:

Operation	Compiler error avoided
ref/out/in/ref readonly parameter reference	CS1628
ref local reference	CS8175
local or parameter of a ref struct type	CS8175
this of a struct	CS1673

Notes for the reviewer

• The check is in the analyzer rather than the code fix: the point of the rule is "you can write this as EnsureInitialized", so when the lambda form cannot exist there is nothing to report. The fixer is only reachable through this diagnostic, so it cannot produce the broken code any more, and no unfixable diagnostic is left behind.
• The ref struct and struct-this cases were not in the original report, but they are the same defect (a value that is legal as an argument and illegal inside a lambda), so they are handled together.
• The check is deliberately conservative: it scans all the descendants, including nested lambdas, so new Foo((ref int x) => ...) is skipped even though hoisting it would compile. That is a missed diagnostic, not a broken fix.
• docs/Rules/MA0173.md documents the exclusion.

Tests

Added to UseLazyInitializerEnsureInitializeAnalyzerTests: six no-diagnostic tests (RefParameter, OutParameter, InParameter, RefLocal, RefStructLocal, StructThis) and a Parameter test that still reports and fixes, to guard against over-restricting the rule.

All six new negative tests were confirmed to fail against the unmodified analyzer and to pass with the change.

Validation

• dotnet build succeeds with no warnings.
• MA0173 tests pass on all five Roslyn versions (4.8, 4.14, 5.0, 5.6, 5.9): 14 passed, 0 failed each.
• Full suite on Roslyn 5.9: 4387 passed, 0 failed, 0 skipped. Full suite on Roslyn 4.8: 4270 passed, 0 failed, 0 skipped.
• dotnet run --project src/DocumentationGenerator exits 0 with no markdown changes, re-run after the documentation edit.