Merge latest F# bits in 15.5 branch

[cartermp]

This is a tracking bug. @KevinRansom recently fixed a bug in assembly resolution which was resulting in a StackOverflow exception: dotnet/fsharp#3658

[cartermp]

@brettfo will be taking care of this in tandem with our insertion of F# tools for Preview 2

[livarcocc]

This should be done now.