[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`).
:+1:. I'll remove the comment and change the priority.