[lldb] Stop searching for a symbol in a pdb by regex

Summary:
It was possible when searching for a symbol by regex in a pdb that an invalid regex would cause an exception on Windows. This updates the code to avoid throwing an exception.

When fixing the exception it was decided there is no reason to search for a symbol in a pdb by regex. To support this, SymbolFilePDB::FindTypes() now only searches for types by name and no longer calls FindTypesByRegEx().

Reviewers: zturner, lldb-commits

Reviewed By: zturner

Subscribers: clayborg

Differential Revision: https://reviews.llvm.org/D41086

llvm-svn: 321344