[dsymutil] Use YAMLIO to dump debug map.

Doing so will allow us to also accept a YAML debug map in input as using
YAMLIO gives us the parsing for free. Being able to have textual debug
maps will in turn allow much more control over the tests, because 1/
no need to check-in a binary containing the debug map and 2/ it will allow
to use the same objects/IR files with made-up debug-maps to test
different scenari.

llvm-svn: 238781