cmd/compile: escape package path for PGO symbol matching

cmd/compile: escape package path for PGO symbol matching

Symbol names in the final executable apply escaping to the final
component of a package path (main in example.com becomes
example%2ecom.main).

ir.PkgFuncName does not perform this escaping, meaning we'd fail to
match functions that are escaped in the profile.

Add ir.LinkFuncName which does perform escaping and use it for PGO.

Fixes #59887.

Change-Id: I10634d63d99d0a6fd2f72b929ab35ea227e1336f
Reviewed-on: https://go-review.googlesource.com/c/go/+/490555
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>