AddDiagnosticPropertyReference should handle augmentations

[DanTup]

The AddDiagnosticPropertyReference fix should handle augmented fields by augmenting the debugFillProperties method in the same class augmentation as the fields.

Currently, the assist/fix is unavailable for fields in augmentations (disabled in https://dart-review.googlesource.com/c/sdk/+/360043 due to the errors noted in https://github.com/dart-lang/sdk/issues/55312).

The debugFillProperties augmentation should call the augmented debugFillProperties.

[DanTup]

I had a quick look through the code for this and I think the required change is probably fairly minor:

If creating a new definition for debugFillProperties in an augmentation and there is already a debugFillProperties in a prior augmentation or the class definition, an augmentation should be emitted instead (eg. it should be marked with augment and should call augmented() instead of super.debugFillProperties)

However it does require that:

• thisType works for augmentations (see https://github.com/dart-lang/sdk/issues/55312#issuecomment-2049987641) so that the Flutter.isDiagnosticable check can work
• augmented() works to calling augmented methods (this wasn't implemented last time I checked, but I think was being worked on)

Some cases that should be tested:

• field is in an augmentation and neither the class or the augmentation have debugFillProperties (we need to produce a new debugFillProperties that is not an augmentation)
• field is in an augmentation and only the class has debugFillProperties (we need to produce a debugFillProperties that is an augmentation)
• field is in an augmentation of an augmentation and only the class has debugFillProperties (ensures we look up the chain to see if we need to produce an augmentation)
• field is in an augmentation of an augmentation and only the intermediate augmentation has debugFillProperties (ensure we look at intermediate augmentations and not only the original class definition)
• field is in an augmentation and the augmentation already has debugFillProperties (ensure we can add to an existing debugFillProperties)
• field is in an augmentation and both the class and the augmentation have debugFillProperties (ensure we add to the augmented debugFillProperties and not the original class definition)