[yaml2obj][test] Move tests to binary format specific subdirectories

Create COFF/, ELF/, and Minidump and move tests there.

Also

* Rename `*.test` to `*.yaml`
* For yaml2obj RUN lines, use `-o %t` instead of `> %t` for consistency.
  We still have tests that check stdout is the default output, e.g.
  multi-doc.test
* Update tests to consistently use `##` for comments.
  `#` is for RUN and CHECK lines.
* Merge symboless-relocation.yaml and invalid-symboless-relocation.yaml to ELF/relocation-implicit-symbol-index.test

Reviewed By: grimar, jhenderson

Differential Revision: https://reviews.llvm.org/D70264