[dyn_modules] Handle implicit uses from const constructors and field initializers of const classes

When const constructor is exposed through a dynamic interface,
dynamic module can create constants with that const constructor and
it can reference everything used in that constructor including default
values of parameters and field initializers. So dynamic interface
annotator should visit bodies of const constructors and add all
references to implicit uses.

Annotator should also visit initializers of instance fields of
classes which can be used in a constant (as they participate in
the constant evaluation too). Kernel trim tool should not remove such
field initializers.

TEST=pkg/dynamic_modules/test/data/const_constructor
Fixes b/418928636

Change-Id: Ie216f3a4257fe5a905b83af8c60dfe8a5b774ecf
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/430002
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Sigmund Cherem <sigmund@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>