ValueMapper: Roll RemapInstruction into Mapper, NFC

Add Mapper::remapInstruction, move the guts of llvm::RemapInstruction
into it, and use the same Mapper for most of the calls to MapValue and
MapMetadata.  There should be no functionality change here.

I left off the call to MapValue that wasn't passing in a Materializer
argument (for basic blocks of PHINodes).  It shouldn't change
functionality either, but I'm suspicious enough to commit separately.

llvm-svn: 265832
GitOrigin-RevId: a574e7a7a4fe727d315685ab4e67d02cf6e76471
2 files changed