Set AppContext.BaseDirectory and the lookup path for AssemblyDirectory to the directory containing the NativeAOT module

[jkoritzinsky]

Fixes #112290
Fixes #90131

We already had most of the components needed to wire this up in the NativeAOT PAL and in the EH DeveloperExperience APIs, so this wasn't as bad as I thought.

[MichalStrehovsky]

Could you add a test for this? I assume since this still doesn't build, it wasn't even manually tested to work, and we definitely don't have test coverage in the tree.

[jkoritzinsky]

Yes I need to still construct a test for this. I'll flip it to draft until I have it ready for review.

[jkoritzinsky]

@MichalStrehovsky I've added a test for this.

[MichalStrehovsky]

The tests are failing but it looks reasonable to me otherwise, thanks!

Just last week I was helping someone in the Windows org who was building a DLL and wondered why they can't load a JSON file next to the DLL with AppContext.BaseDirectory.

I wonder if we should doc this as a breaking change, someone might use this and it would be nice to have guidance ready (just use the directory of the Environment.ProcessPath).

[jkoritzinsky]

I'll mark this as a breaking change and file the doc after I fix the test and merge.

[elinor-fung]

It might also be good to add a note to the DllImportSearchPath.AssemblyDirectory doc about Native AOT libraries.

[MichalStrehovsky]

Native AOT outerloop runs are broken: many tests failing with "The path must be absolute":

[FAIL] Microsoft.Extensions.Hosting.Tests.HostBuilderTests.DefaultConfigIsMutable
System.ArgumentException : The path must be absolute. (Parameter 'root')
   at Microsoft.Extensions.FileProviders.PhysicalFileProvider..ctor(String, ExclusionFilters) + 0xe0
   at Microsoft.Extensions.Hosting.HostBuilder.CreateHostingEnvironment(IConfiguration) + 0x118
   at Microsoft.Extensions.Hosting.HostBuilder.Build() + 0x3b
   at Microsoft.Extensions.Hosting.Tests.HostBuilderTests.DefaultConfigIsMutable() + 0x2c
   at Microsoft.Extensions.Hosting.Unit!<BaseAddress>+0x1db881b
   at System.Reflection.DynamicInvokeInfo.Invoke(Object, IntPtr, Object[], BinderBundle, Boolean) + 0x118

If I'm reading this right the problem is that we somehow end up using the path of argv[0] as the AppContext.BaseDirectory, but that can be a relative path relative to the current directory at process start. (I didn't actually try to debug this, I just worked backwards from the newly added test for BaseDirectory that uses argv[0] as the expected value.)

If this cannot be fixed quickly, I'd prefer this to be reverted because it's failing 100 tests and it's hard to keep an eye on outerloop with so many failures.

[MichalStrehovsky]

Sample outerloop run with the failures: https://dev.azure.com/dnceng-public/public/_build/results?buildId=968880&view=logs&j=7e7cde7f-4669-5f41-976b-370a74291e60&t=e3f1bc70-511c-5e38-2600-aec10f79e344

[jkoritzinsky]

I'll take a look today and if I can't fix it I'll revert it.