Add encode and decode methods to InlineInfo and document encoding format to the GSYM...

Add encode and decode methods to InlineInfo and document encoding format to the GSYM file format.

This patch adds the ability to encode and decode InlineInfo objects and adds test coverage. Error handling is introduced in the encoding and decoding which will be used from here on out for remaining patches.

Differential Revision: https://reviews.llvm.org/D66600

llvm-svn: 370936