Use EnumSerializer for explicitly serializable enum instead of auto-generated one

[qwwdfsad]

And inject a customized descriptor (or use generated by EnumSerializer if enum doesn't have customized annotations).

Multiple reasons to do it:

* Less bytecode (not a big deal, in fact)
* Completely **identical** behaviour of `@Serializable enum class Foo { ... }` and `enum class Foo`
* Ability to do fixes, changes and performance optimization on the library level without changes in the plugin