cmd/compile/internal/syntax: rename ErrorMap to CommentMap, make more flexible

cmd/compile/internal/syntax: rename ErrorMap to CommentMap, make more flexible

Change the ErrorMap function to collect all comments with a comment
text that matches a given regexp pattern. Also rename it to CommentMap.

Adjust uses and corresponding test.

Adjust various type-checker tests with incorrect ERROR patterns.

For #51006.

Change-Id: I749e8f31b532edbf8568f27ba1546dc849efd143
Reviewed-on: https://go-review.googlesource.com/c/go/+/456155
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Cherry Mui <cherryyz@google.com>