Make F# Analyzer API independent of FCS?

I've been thinking about [the problem of binary compatibility for F# analyzers](https://github.com/fsharp/fslang-design/blob/master/tooling/FST-1033-analyzers.md), in the context of trying to get F# analyzers available in all F# tooling.

This is a blocking problem for incorporation of analyzers into the Visual F# Tools. This applies even if those tools switch to FsAutoComplete - all analyzers must still be loadable into all future iterations of F# tooling.

The main issue is binary compatibility for the information being drawn from the FCS API (FSharpSymbol etc.). I am wondering if we might consider making this F# Analyzer API **completely independent of FCS**. When hosted, FSharpAutoComplete would provide necessary shims.

This would mean the F# Analyzer API would include abstract types like IFSharpSymbol, ISyntaxTree and so on. It would be a complete self-contained, zero-dependency facade over all the information analyzers typically require.

FCS could then take a dependency on this component (which I called FSharp.Compiler.Analyzers in the link above).