Baseline struct lifting tests

[333fred]

In order to make the next PR easier to read, I've started by baselining the existing struct lifting tests with current runtime async behavior; this is an entirely mechanical change and I've made no attempt to validate that the resulting code is good (it likely isn't in most cases). The next PR should implement proper struct lifting, and having a good set of baselines will make it easier to observe the changes in IL behavior, rather than trying to understand the entire IL all at once.

Relates to test plan #75960

[333fred]

At about 2/3rds of the way through updating the tests, I got fed up with adding new things to the runtime-async stub of corelib. 10p5 has the necessary support, so I have a PR (out)[https://github.com/jaredpar/basic-reference-assemblies/pull/73/] to update Basic.Reference.Assemblies with 10p6 and will unskip the relevant tests when we have that and can consume them here.

[jcouv]

        verifier.VerifyIL("Test.G()", """

This doesn't look like it's validating the intended method. Same comment applies in other places below

---

Refers to: src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncSpillTests.cs:1437 in c4e8111. [](commit_id = c4e8111, deletion_comment = False)

[jcouv]

        verifier.VerifyIL("Test.G()", """

Same here

---

Refers to: src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncSpillTests.cs:1907 in c4e8111. [](commit_id = c4e8111, deletion_comment = False)

[jcouv]

        verifier.VerifyIL("Test.G()", """

Same here

---

Refers to: src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncSpillTests.cs:2085 in c4e8111. [](commit_id = c4e8111, deletion_comment = False)

[jcouv]

            ILVerifyMessage = $$"""

I probably asked in a previous PR, but I can't find an issue in runtime repo for addressing these ILVerify errors. What's the link?
Personally, I'd link it everywhere, but I could settle for at least having it in first occurrence of each specific error in the file (ie. one for Task and one for Task scenario)

---

Refers to: src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncSpillTests.cs:2385 in c4e8111. [](commit_id = c4e8111, deletion_comment = False)

[jcouv]

public async Task Run()

Consider refactoring the test code, so that we have easier to review IL blobs. In this case, I'd probably extract the logic for arr1 and arr2 to helper methods. This will separate concerns.
This applies to some other tests as well

---

Refers to: src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncSpillTests.cs:4671 in c4e8111. [](commit_id = c4e8111, deletion_comment = False)

[jcouv]

        verifier.VerifyIL("c1.Goo1()", """

Consider also verifying S1.Goo1 (involves ref)

---

Refers to: src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenAsyncSpillTests.cs:7803 in c4e8111. [](commit_id = c4e8111, deletion_comment = False)

[jcouv]

Done with review (commit 8)

[dotnet-policy-service]

This PR modifies public API files. Please follow the instructions at https://github.com/dotnet/roslyn/blob/main/docs/contributing/API%20Review%20Process.md for ensuring all public APIs are reviewed before merging.

[jcouv]

LGTM Thanks (commit 15)

[RikkiGibson]

I did only a cursory review of CodeGenAsyncSpillTests.cs, but did fully review the others. Changes LGTM.