BreakpadRecords: Address post-commit feedback

Summary:
This addresses the issues raised in D56844. It removes the accessors from the
breakpad record structures by making the fields public. Also, I refactor the
UUID parsing code to remove hard-coded constants.

Reviewers: lemo

Subscribers: clayborg, lldb-commits

Differential Revision: https://reviews.llvm.org/D57037

llvm-svn: 352021