Support build-ids of other sizes than 16 in UUID::SetFromStringRef

Support build-ids of other sizes than 16 in UUID::SetFromStringRef

SBTarget::AddModule currently handles the UUID parameter in a very
weird way: UUIDs with more than 16 bytes are trimmed to 16 bytes. On
the other hand, shorter-than-16-bytes UUIDs are completely ignored. In
this patch, we change the parsing code to handle UUIDs of arbitrary
size.

To support arbitrary size UUIDs in SBTarget::AddModule, this patch
changes UUID::SetFromStringRef to parse UUIDs of arbitrary length. We
subtly change the semantics of SetFromStringRef - SetFromStringRef now
only succeeds if the entire input is consumed to prevent some
prefix-parsing confusion. This is up for discussion, but I believe
this is more consistent - we always return false for invalid UUIDs
rather than sometimes truncating to a valid prefix. Also, all the
call-sites except the API and interpreter seem to expect to consume
the entire input.

This also adds tests for adding existing modules 4-, 16-, and 20-byte
build-ids. Finally, we took the liberty of testing the minidump
scenario we care about - removing placeholder module from minidump and
replacing it with the real module.

Reviewed By: labath, friss

Differential Revision: https://reviews.llvm.org/D80755