ignore unused_field for __mouse__ in generated files

[chalin]

So that we can avoid this analyzer hint:

  hint • The value of the field '__mouse__' isn't used at test/app_po.g.dart:128:19 • unused_field

cc @kevmoo @kwalrath

[chalin]

@mk13 - do you think that this can be fixed for 3.0.0 final?

At a minimum, an ignore directive should do it:

  PageLoaderMouse __mouse__; // ignore: unused_field

[mk13]

I'll add this in with the 3.0.0 release.

[mk13]

Done, will be published with 3.0.0