Match versioned OS platform attributes in CoreCLR PInvokeCollector, add regression test

[Copilot]

Follow-up to #132300: the CoreCLR generator's platform-attribute filter still compared SupportedOSPlatform/UnsupportedOSPlatform strings to _targetOS with exact equality, so versioned attributes like [SupportedOSPlatform("browser1.0")] were treated as non-matching on that path (mono's collector was already fixed).

CoreCLR collector fix

• Duplicated the MatchesTargetOS helper (with the NETFRAMEWORK conditional for net472) into src/tasks/WasmAppBuilder/coreclr/PInvokeCollector.cs, per maintainer preference to keep the collectors independent rather than share code.
• EvaluatePlatformAttributes now calls MatchesTargetOS instead of exact string comparison for both attributes.
• src/tasks/WasmAppBuilder/mono/PInvokeCollector.cs is unchanged.

if (cattr.AttributeType.FullName == "System.Runtime.Versioning.UnsupportedOSPlatformAttribute" &&
    cattr.ConstructorArguments.Count > 0 &&
    MatchesTargetOS(cattr.ConstructorArguments[0].Value?.ToString()))
{
    return PlatformSupport.Unsupported;
}

Regression test

• Added VersionedOSPlatformPInvokeIsIncluded to PInvokeTableGeneratorTests in src/mono/wasm/Wasm.Build.Tests.
• New test asset declares a P/Invoke annotated [SupportedOSPlatform("browser1.0")] (must match TargetOS=browser) alongside one annotated [SupportedOSPlatform("windows1.0")] (must not match).
• Asserts the browser-versioned entry is present in the generated pinvoke table and the windows-versioned one is absent, then runs the app to confirm the included P/Invoke is callable at runtime.

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[Copilot]

Pull request overview

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