Rename Jackson-specific Json… annotations and classes to Jackson…

[wilkinsona]

There are a number of classes in org.springframework.boot.jackson with names that suggest they're applicable to JSON in general and not just when using Jackson. They're also not strictly tied to JSON (for example, a @JacksonMixin could influence Jackson's XML output) so the current names are arguably misleading in two ways.

4.0 gives us an opportunity to make the names less misleading:

Current name	Proposed name
@JsonComponent	@JacksonComponent
JsonComponentModule	JacksonComponentModule
@JsonMixin	@JacksonMixin
JsonMixinModule	JacksonMixinModule
JsonMixinModuleEntries	JacksonMixinModuleEntries

[philwebb]

We discussed this today and we're going to rename the types.