PullRequest: fastr/1260

[GR-6959] [GR-6840] Strange interop behaviour of R complex number and other fixes in FastR message resolution.

PullRequest: fastr/1250

PullRequest: fastr/1259

PullRequest: fastr/1258

There is fast-path implementation that handles single thread case until
another thread appears in which case we transfer to interpreter, invalidate,
and fallback to more generic implementation.

PullRequest: fastr/1248

PullRequest: fastr/1257

remove unnecessary implicit Raw/Complex casts from RTypes and ensure wrapping of scalar vectors in FFIWrapNode

- simplify MR tests