Beforecompile

[KevinRansom]

Fixes #16771

For years CompileBefore and CompileAfter have been used to position generated files in the FSharp project build.

However, they are not WellKnown supported dotnet sdk collections. This PR changes this by allowing BeforeCompile and AfterCompile to be specified as metadata attached to CompileItems.

Note:

1. In order to maintain compatibility with existing projects that may use CompileBefore and CompileAfter we maintain support for them
2. The existing FSharp repo build will continue to use CompileBefore and CompileAfter collections, to avoid rewriting their build targets.

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[T-Gro]

Does this need docs changes?