[FrameworkBundle] make GetSetMethodNormalizer available by default

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | very limited
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT
| Doc PR        | not yet

The `GetSetMethodNormalizer` has not been enabled by default in #6815 because it was broken by design. Since #12098 has been merged, circular references are handled and that normalizer cannot breaks applications.
This PR makes that normalizer automatically available when the serializer is enabled. To keep BC, I've set a "high" priority for this service (higher than the default `0`).
talking about keeping BC in the comment is the wrong explanation. The reason to make it last (even without BC concern) is that it will report (nearly) any object as supported, so it should give other normalizer a chance to pick the object first.