Move MathNet.Numerics out of RvmSharp

[minorai]

First part of 3-part change to make rvmsharp useful in Unity again,

Motivation

• Use RvmSharp in Unity
• Prepare for improvements in tesselation, and connection detection in RvmSharp

Changes

• none of the Math extension methods are used in rvmsharp anyway and do not belong there imho, moved to CadRvmConverter
• changed all uint for mesh vertex indexing to int, there is little benefit of using uint (the only one being is that you cannot assign negative number, but that is not really a benefit, given that out-of-bound values are still possible), but int will remove Unity exception on internal Rvm array copy without cast, and will remove multiple linq cast throughout the code, reducing complexity
• moved IStringInternPool to own assembly to separate implementation from interface. Snyk pleasing change in Commons is causing issues in Unity.

Testing

• Pipeline: since this is a refactoring, all existing tests must pass, no new actual code is written yet
• Unity: TBW

[Strepto]

@minorai You should fix the merge confligcts this to allow the builds to run. Rest of it seems ok to me (y)