It's a bug if a class has more than one `@AbiSpecificIntegerMapping`
annotation. Reflect this in the return type of method for getting the
annotation and issue a diagnostic if the invariant doesn't hold.
The invariant is checked by `_FfiDefinitionTransformer`.
Change-Id: Iadf4636090c6ec814f623c9245b3a1fe8b466b4b
Tested: Unit tests written with all ABI specific integer types.
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/268105
Reviewed-by: Daco Harkes <dacoharkes@google.com>
Commit-Queue: Jackson Gardner <jacksongardner@google.com>
Reviewed-by: Ömer Ağacan <omersa@google.com>
Jackson Gardner
81a63dafe5