cmd/compile: adjust debug/gosym to deal with instantiated types/funcs/methods

This changes debug/gosym so it can deal with instantiated
types/funcs/methods. I also added tests for instantiated names. My
assumption is that the concatenation of PackageName, ReceiverName, and
BaseName in order should cover the entire symbol name, so either the
ReceiverName or the BaseName should include any bracketed information
(either the instantiation of the receiver of a method or the
instantiation of function).

This can provide a model for how to parse instantiated functions and
method names.

Fixes #48032

Change-Id: I476781de2d6fc096efbb4be85c197d6f1cafac21
Reviewed-on: https://go-review.googlesource.com/c/go/+/354689


Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>