Add rust demangling support
Review Request #2012 - Created June 20, 2019 and submitted
This adds the ability to demangle rust symbols up to version 1.35 (the most recent release) to our native demangling library (used by mdb(1), dis(1), among others). Starting with the upcoming 1.36 rust release, the mangling system changes, but does so in a manner that doesn't affect demangling of things using the current mangling scheme.
Included test cases were run, which worked successfully.
Include Joyent OS-7695
Revision 2 (+1224 -51)