MC: rename WinCOFFStreamer and move declaration out-of-line

MC: rename WinCOFFStreamer and move declaration out-of-line

This is in preparation for promoting WinCOFFStreamer to a base class which will
be shared by the X86 and ARM specific target COFF streamers.  Also add a new
getOrCreateSymbolData interface (like MCELFStreamer) for the ARM COFF Streamer.
This makes the COFFStreamer more similar to the ELFStreamer.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207343 91177308-0d34-0410-b5e6-96231b3b80d8