[parser] Ensure that list and map pattern parsing always makes progress.

In rare circumstances involving syntax errors, the `parsePattern`
method inserts a synthetic token but does not consume any
tokens. Usually when this happens it's not a problem, because whatever
method is calling `parsePattern` consumes some tokens, so the parser
always makes progress. However, when parsing list patterns, after
calling `parsePattern`, the parser would look for a `,`, and if it
didn't find one, it would supply a synthetic `,` and call
`parsePattern` again, resulting in an infinite loop. A similar
situation happened with map patterns, though the situation was more
complex because in between the calls to `parsePattern`, the parser
would also create synthetic key expressions and `:`s.

To fix the problem, when parsing a list or map pattern, after the call
to `parsePattern`, the parser checks whether any tokens were
consumed. If no tokens were consumed, it ignores the next token from
the input stream in order to make progress.

I also investigated whether there were similar issues with
parenthesized/record patterns and switch expressions, since those
constructs also consist of a sequence of patterns separated by tokens
and other things that could in principle be supplied
synthetically. Fortunately, parser recovery doesn't get into an
infinite loop in those cases, so I didn't make any further
changes. But I did include test cases to make sure.

Fixes #52352.

Bug: https://github.com/dart-lang/sdk/issues/52352
Change-Id: Idc8140236f6054deb1fd3c862036fe47dd84f30b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/302803
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>