Enable HotReload tests for FieldRVA

[AaronRobinsonMSFT]

Support was added in #114463, but we are awaiting updates from Roslyn. After the update we also will need to enabled the tests.

runtime/src/libraries/System.Runtime.Loader/tests/ApplyUpdateTest.cs

Lines 326 to 329 in 40f209c

	// FieldRVA update tests are not supported on the Mono runtime.
	//[ConditionalFact(typeof(ApplyUpdateUtil), nameof (ApplyUpdateUtil.IsSupported), nameof (ApplyUpdateUtil.IsNotMonoRuntime))]
	//[ActiveIssue("https://github.com/dotnet/runtime/issues/54617", typeof(PlatformDetection), nameof(PlatformDetection.IsBrowser), nameof(PlatformDetection.IsMonoAOT))]
	void TestAddFieldRVA()

Also uncomment build failures involving stackalloc.

runtime/src/libraries/System.Runtime.Loader/tests/ApplyUpdateTest.cs

Lines 340 to 341 in 40f209c

	// var lsarosLen = ApplyUpdate.Test.AddFieldRVA.LocalStackAllocReadOnlySpan();
	// Assert.Equal(-1, mfaLen);

runtime/src/libraries/System.Runtime.Loader/tests/ApplyUpdateTest.cs

Lines 355 to 356 in 40f209c

	// var lsarosLen = ApplyUpdate.Test.AddFieldRVA.LocalStackAllocReadOnlySpan();
	// Assert.Equal(5, mfaLen);

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[AaronRobinsonMSFT]

/cc @tmat

[jkotas]

Also, apply additional feedback: https://github.com/dotnet/runtime/pull/114463/files#r2048201314