Refactor GetCSharpStyleIndexedExtensionMembersForTyconRef: unify logic

[DedSec256]

Remove code duplicates, generalize check

If you believe that release notes are not necessary for this PR, please add NO_RELEASE_NOTES label to the pull request.

[github-actions]

⚠️ Release notes required, but author opted out

Warning

Author opted out of release notes, check is disabled for this pull request.
cc @dotnet/fsharp-team-msft

[psfinaki]

Can you please point me out where this is tested? Just to be more confident about the refactoring :)

[edgarfgp]

Can you please point me out where this is tested? Just to be more confident about the refactoring :)

We tests are here https://github.com/dotnet/fsharp/blob/main/tests/FSharp.Compiler.ComponentTests/Language/ExtensionMethodTests.fs

Edit: Implemented feature Allow extension methods without type attribute PR #13839

[DedSec256]

@psfinaki, the most important test is that this repository is completely built (including VisualFSharp), because, as the practice of my other PR (#16168) shows, the dotnet/fsharp project contains more interesting cases in its code than there are in tests.

There are also tests for old C#-compatible extensions, for example, https://github.com/dotnet/fsharp/blob/main/tests/fsharp/Compiler/Language/StaticNameResolutionTests.fs

and for new F# 8 CSharpExtensionAttributeNotRequired feature

fsharp/tests/fsharp/Compiler/Language/OpenTypeDeclarationTests.fs

Line 1476 in 31f3d2b

let ``Opened types do allow unqualified access to C#-style extension methods if type has no [<Extension>] attribute`` () =

[psfinaki]

Alright, yeah, thanks for the links :)