Prefer module methods over Any instance ones

[JaroslavTulach]

Pull Request Description

While working on #12031 it turned out that Meta.is_a and extension method Any.is_a clash. It makes little sense to treat module's associated type as a value, and as such let's prefer static methods for these associated types. By doing this we refine:

• Invoke instance methods for Any overrides #6441
• Always call instance methods on Any #7033

those PRs define preference of Any instance methods over regular types static method ones. E.g. with the integration of this PR the behavior depends on type being associated with a module or being a regular type. That's desirable as regular types often refine instance methods defined on Any while types associated with a module override nothing, but rather serve as a container for module (static) methods.

Checklist

Please ensure that the following checklist has been satisfied before submitting the PR:

• The documentation has been updated, if necessary.
• All code follows the
  Scala,
  Java,
  style guides. In case you are using a language not listed above, follow the Rust style guide.
• Unit tests have been written where possible.

[Akirathan]

Nice docs and tests