Remove DWARFExpression::LocationListSize

Summary:
The only reason for this function's existance is so that we could pass
the correct size into the DWARFExpression constructor. However, there is
no harm in passing the entire data extractor into the DWARFExpression,
since the same code is performing the size determination as well as the
subsequent parse. So, if we get malformed input or there's a bug in the
parser, we'd compute the wrong size anyway.

Additionally, reducing the number of entry points into the location list
parsing machinery makes it easier to switch the llvm debug_loc(lists)
parsers.

While inside, I added a couple of tests for invalid location list
handling.

Reviewers: JDevlieghere, clayborg

Subscribers: aprantl, javed.absar, kristof.beyls, lldb-commits

Differential Revision: https://reviews.llvm.org/D66789

llvm-svn: 370373