[DedSec256]

ProjectSnapshotBase stored its source files and referenced projects as lists. The TransparentCompiler usually needs them as arrays, so the code kept converting back and forth:

• Every producer of a snapshot stage (LoadSources, parseSourceFiles, parseSourceFilesExceptImplFilesWithSignatures, FromOptions, GetProjectSnapshotFromScript) gets an array from MultipleDiagnosticsLoggers.Parallel and turned it into a list with Array.toList. parseSourceFilesExceptImplFilesWithSignatures then turned it back with List.toArray.
• ComputeTcIntermediate and the ArtificialImplFile branch of processGraphNode read the file by index, projectSnapshot.SourceFiles[index]. On a list each read walks the list, which makes type checking a project quadratic in its file count.
• List.last, .Length and List.tryItem are used in several places.

This PR makes sourceFiles and referencedProjects arrays.

Breaking change (experimental API)

The public surface of FSharpProjectSnapshot changes:

• SourceFiles: FSharpFileSnapshot[]
• ReferencedProjects: FSharpReferencedProjectSnapshot[]
• Create(..., sourceFiles: FSharpFileSnapshot[], ..., referencedProjects: FSharpReferencedProjectSnapshot[], ...)
• Replace(changedSourceFiles: FSharpFileSnapshot[])

The API is marked [<Experimental>]. Callers have to pass and consume arrays instead of lists. The surface area baseline is updated.

[github-actions]

✅ Release notes checked

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✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
`src/Compiler`	docs/release-notes/.FSharp.Compiler.Service/11.0.200.md
`vsintegration/src`	docs/release-notes/.VisualStudio/18.vNext.md