go/types, types2: consolidate testdata/fixedbugs test files

go/types, types2: consolidate testdata/fixedbugs test files

Use the go/types version of testdata/fixedbugs tests where diffs
are only in the error positions (the types2 test harness allows
for some position tolerance). Consolidate files where there are
other minor differences.

Add files to respective directories if they only existed for
one of the type checkers.

Move types2-only test issue47996.go out of testdata/fixedbugs
into testdata. Making it work for both type checkers requires
some more work.

With this CL, the testdata/fixedbugs files are identical between
the two type checkers.

For #54511.

Change-Id: I0d67f0db75ad1743c62da9181a6d0032c8bdb728
Reviewed-on: https://go-review.googlesource.com/c/go/+/427236
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>