Add compiler-generated code tests for NativeAot

[sbomer]

This makes progress towards #68786. It is still hitting issues such as #68688 and #77455, which are referenced in the test comments.

Also fixes an issue where warnings were not produced for ldftn. The test changes are a modified copy of tests from the linker codebase. See dotnet/linker#3085 for the included changes.

[tlakollo]

Looks good to me. Nice catch on the Release vs Debug releases. Did you try the checked version too? I'm guessing it behaves like the Debug one

[sbomer]

I don't think there is a checked configuration for managed code by default - only for native code in dotnet/runtime. Your comment made me realize I didn't add the release mode tests to this PR yet, thanks!

[MichalStrehovsky]

I don't think there is a checked configuration for managed code by default

We do support building the tools directory as checked:

runtime/src/coreclr/tools/Directory.Build.props

Lines 11 to 15 in 7b5ab35

	<!-- MSBuild doesn't understand the Checked configuration -->
	<PropertyGroup Condition="'$(Configuration)' == 'Checked'">
	<Optimize Condition="'$(Optimize)' == ''">true</Optimize>
	<DefineConstants>DEBUG;$(DefineConstants)</DefineConstants>
	</PropertyGroup>

It may become less relevant if linker tests get moved out of the coreclr test tree in the future (we don't need to support checked outside the coreclr tree).

[sbomer]

We do support building the tools directory as checked

Good to know, thanks! For the tests I added, there should be no difference since we compile the testcase in-proc in a way that doesn't depend on the tools config.

[vitek-karas]

Couple of comments, but nothing blocking.