[vm] Fix ArgumentsDescriptor uses in DoArgumentTypesMatch.

Use of PositionalCount() and PositionAt() as indices in the arguments
array must account for the type arguments if present. Otherwise, we'll
either skip checking the last positional argument (in the former case)
or check against the wrong arguments (in the latter case).

In nosuchmethod_forwarding_arguments_test.dart, add cases that check for
the above mistakes.

In require_named_args_strong_test.dart, use the more specific
throwsTypeError or throwsNoSuchMethod checks instead of the generic
throwsError to ensure the correct error is thrown.

TEST=Changed tests to add extra cases for failures that can happen.

Cq-Include-Trybots: luci.dart.try:vm-kernel-linux-debug-x64-try,vm-kernel-nnbd-linux-debug-x64-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-nnbd-linux-debug-x64-try
Change-Id: If5e6c310d36d244bb0650ded54e32e583732584e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/171947
Reviewed-by: Martin Kustermann <kustermann@google.com>
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Tess Strickland <sstrickl@google.com>