Rename SerializerProvider as SerializationContext

[cowtowncoder]

Something that should have been done during 1.x->2.0 major version upgrade but better late than never: due to historical reasons (serialization implemented before deserialization), context object naming is inconsistent. We have:

• DeseralizationContext for deserialization
• SerializerProvider for serialization

Latter may have made sense in 0.9.4 since the primary reason was access to child serializers (and this is still an importan use case); but conceptually it is a context object, and has expanded a lot in functionality.
So let's fix this naming discrepancy in 3.0.
(yes, this will result in lots of changes across the whole codebase)

EDIT: Related renaming:

• JsonFormatVisitorWithSerializerProvider -> JsonFormatVisitorWithSerializationContext

[cowtowncoder]

/cc @JooHyukKim @pjfanning @k163377 I will be doing this major renaming now for 3.0/master. Apologies for short term disruption. This is part of my focusing again on making 3.0 actual reality. Will try to keep everyone informed.

This work f.ex is part of JSTEP-6.
I will also try to update documentation.

[cowtowncoder]

So far I have update almost all modules, including Kotlin but not Scala (but I think @pjfanning is already doing or has done that). One remaining failure is for jackson-datatypes-collection, some odd code generation issue). But we are mostly done I think.

[JooHyukKim]

Great work on the work itself and for focusing on 3.0 version!

[cowtowncoder]

I am trying to go back to documentation, and updated

https://github.com/FasterXML/jackson-future-ideas/wiki/JSTEP

(plus JSTEPs referenced).

But need to think of how to better combine different pieces so they would not be so disjoint.
Might end up creating one more wiki page on jackson-future-ideas for an overview of what goes in 3.0 planning. I don't think there is a lot we need to do (def not everything labelled with 3.x :) ), but it'd be good to have a sort of list of approximately what is still needed.