test: re-enable most go/tests that were disabled because of types2 differences

I made the default be that, where there are differences between types2
and -G=0 error messages, we want errorcheck tests to pass types2.
Typically, we can get errorcheck to pass on types2 and -G=0 if they give
the same number of error messages on the same lines, just different
wording. If they give a different number of error messages, then I made
types2 pass. I added an exception list for -G=0 to cover those cases
where -G=0 and types give different numbers of error messages.

Because types2 does not run if there are syntax errors, for several
tests, I had to split the tests into two parts in order to get all the
indicated errors to be reported in types2 (bug228.go, bug388.go,
issue11610.go, issue14520.go)

I tried to preserve the GCCGO labeling correctly (but may have gotten
some wrong). When types2 now matches where a GCCGO error previously
occurred, I transformed GCCGO_ERROR -> ERROR. When types2 no longer
reports an error in a certain place, I transformed ERROR -> GCCGO_ERROR.
When types2 reports an error in a new place, I used GC_ERROR.

The remaining entries in types2Failures are things that I think we
probably still need to fix - either actually missing errors in types2,
or cases where types2 gives worse errors than -G=0.

Change-Id: I7f01e82b322b16094096b67d7ed2bb39b410c34f
Reviewed-on: https://go-review.googlesource.com/c/go/+/372854
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

test/fixedbugs/issue7525c.go

@@ -8,6 +8,6 @@
 
 package main
 
-var z struct {
-	e [cap(z.e)]int // ERROR "array bound|typechecking loop|invalid array"
+var z struct { // GC_ERROR "initialization loop for z"
+	e [cap(z.e)]int // GCCGO_ERROR "array bound|typechecking loop|invalid array"
 }