Add `@JsonDeserializeAs` (split off databind `@JsonDeserialize`)

[ooraini]

JsonDeserialize and JsonSerialize are part of databind since they depend on classes in databind JsonSerializer..etc. But the as part of the annotations doesn't. It would be useful as a standalone annotations for project that don't want to depend on databind.

If it makes a sense and it's possible to split the annotations into @JsonDeserializeAs and @JsonSerializeAs in the jackson-annotation package.

[cowtowncoder]

First of all: thank you for suggesting the idea.

Unfortunately: while idea makes sense, challenge is timing, compatibility handling.
Problem being that the old and new annotations must be supported, information combined etc.
I agree that splitting would (have) be(en) the right way to go if done earlier.
Change like this must go in next minor version (2.21) as per SemVer and 2.20 was just released, to be used by 3.0.0.

Then again: this could perhaps be done for 2.21.x/3.1.x timeline... which would work much better, timeline-wise.

[cowtowncoder]

Note: cleaved @JsonSerialize into separate issue (#324) this remains for @JsonDeserialize(As)