Notify users when popular but controversial lints are compatible with how they are writing code

[jacob314]

Motivation:
About 35% of Dart users write code where all locals are inferred but only 6% have enabled the lint omit_local_variable_types.
About 19% of Dart users write code where no locals are inferred but only about 4% have enabled the lint always_specify_types.

If we had a list of "good but controversial" lints we could automatically suggest the lints for cases where >= X% of cases in a project are already consistent with the lint.

Q: Why bother as the user is already generally following the lint on their own?
A: Because it will save users time code reviewing and manually checking that their code conforms to the lints. Without some way of promoting lints that could be useful, the only lints that make a significant impact of user productivity are ones in a recommended set.

Related lint discussion with context on how frequently existing code follows some of the controversial lints: dart-lang/linter#4853