WIP: Verify -gsimple-template-names=mangled values

WIP: Verify -gsimple-template-names=mangled values

Clang will encode names that should be able to be simplified as
"_STNname|<template, args>" (eg: "_STNt1|<int>") - this verification
mode will detect these names, decode them, create the original name
("t1<int>") and the simple name ("t1") - letting the simple name run
through the usual rebuilding logic - then compare the two sources of the
full name - the rebuilt and the _STN encoding.

This helps ensure that -gsimple-template-names is lossless.