[TableGen] Remove the use of global Record state

This commits removes TableGens reliance on managed static global record state
by moving the RecordContext into the RecordKeeper. The RecordKeeper is now
treated similarly to a (LLVM|MLIR|etc)Context object and is passed to static
construction functions. This is an important step forward in removing TableGens
reliance on global state, and in a followup will allow for users that parse tablegen
to parse multiple tablegen files without worrying about Record lifetime.

Differential Revision: https://reviews.llvm.org/D125276