cmd/compile: fix //go:uintptrescapes for basic method calls

The logic for keeping arguments alive for calls to //go:uintptrescapes
functions was only applying to direct function calls. This CL changes
it to also apply to direct method calls, which should address most
uses of Proc.Call and LazyProc.Call.

It's still an open question (#34684) whether other call forms (e.g.,
method expressions, or indirect calls via function values, method
values, or interfaces).

Fixes #34474.

Change-Id: I874f97145972b0e237a4c9e8926156298f4d6ce0
Reviewed-on: https://go-review.googlesource.com/c/go/+/198043


Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>