[Repo Assist] feat: add code fix for wildcard _ -> in pattern match for FS0043

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🤖 This is an automated PR from Repo Assist, created on behalf of @Krzysztof-Cieslak's request to rebase PR #1157.

Summary

This PR rebases the changes from #1157 by @jkone27 onto current main. It adds a code fix that suggests replacing the invalid |-> operator with the correct wildcard pattern | _ -> in a match expression when the F# compiler diagnostic FS0043 is raised.

Related issue: dotnet/fsharp#15748

Changes

• src/FsAutoComplete/CodeFixes/AddMissingWildcardOperator.fs — new code fix implementation
• src/FsAutoComplete/CodeFixes/AddMissingWildcardOperator.fsi — signature file
• src/FsAutoComplete/LspServers/AdaptiveServerState.fs — register the new code fix
• test/FsAutoComplete.Tests.Lsp/CodeFixTests/AddMissingWildcardOperatorTests.fs — test for the code fix
• test/FsAutoComplete.Tests.Lsp/CodeFixTests/Tests.fs — register test module

Rebase notes

The following adaptations were made when rebasing onto current main:

• FsAutoComplete.Lsp.fs was removed from the codebase — that change was dropped
• Code fix registration was moved from AdaptiveFSharpLspServer.fs to AdaptiveServerState.fs
• ftestCaseAsync → testCaseAsync (focused test markers cause CI failures)
• Fixed unused variable lineStr → _lineStr (F# compiler error FS1182)

Test Status

✅ Build succeeded (dotnet build src/FsAutoComplete/FsAutoComplete.fsproj)
✅ Code formatted with dotnet fantomas

Closes #1157

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