cmd/go: convert tests using testdata/src/(xtestonly|cgotest) to script framework

Part of converting all tests to script framework to improve
test parallelism.

Updates #36320
Updates #17751

Change-Id: I3465cad1b0ba0d912067429146f1cb0668d5aa6b
Reviewed-on: https://go-review.googlesource.com/c/go/+/214284


Reviewed-by: Jay Conrod <jayconrod@google.com>