Checks to see if a JS interop member is correctly annotated with
the `external` keyword. If it is not, it must be one of several
exceptions to be allowed.
This CL also changes static errors to first check for `JS` and
`external` before processing the member as a JS interop member.
This makes it clearer whether a member is a JS member.
Change-Id: I412eeafbfe8773847bfb9c864e4fb9b65e2d632a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/158083
Commit-Queue: Srujan Gaddam <srujzs@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Srujan Gaddam