Cleanup headers for BinaryFormat

A few header removal, some forward declarations. As usual, this can
break your build due to false dependencies, the most notable change are:

- "llvm/BinaryFormat/AMDGPUMetadataVerifier.h" no longer includes "llvm/BinaryFormat/MsgPackDocument.h"

The impact on generated preprocessed lines for LLVMBinaryFormat is
pretty nice:

$ clang++ -E  -Iinclude -I../llvm/include ../llvm/lib/BinaryFormat/*.cpp -std=c++14 -fno-rtti -fno-exceptions | wc -l
before this patch: 705281
after this patch: 751456

Discourse thread on the topic: https://llvm.discourse.group/t/include-what-you-use-include-cleanup