Add Array node#set methods

[TarekkMA]

Closes #3154

The issue I see is that public JsonNode set(int index, JsonNode value) doesn't return the ArrayNode back to the caller.

I don't know if we should add setNode version that will be able to do chaining.

[cowtowncoder]

Thank you!
Please rebase against 2.13: master is for Jackson 3.0 which will not be out for a while.

Also: if I haven't yet asked for a CLA, I would need one from here:

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

(if I already have gotten one no need to send again; this only needs to be done once)

The usual way is to print it, fill & sign, scan/photo, email to info at fasterxml dot com.

[TarekkMA]

Oh, I did rebase against it but forget to select the correct branch when opening a PR. it should be correct now.

I will sign the CLA and email it today.

[cowtowncoder]

CLA received so that's good.

I will be out of town untl next tuesday so will not be able to merge this in until then, but will look into it afterwards.
Thank you very much for contributing the idea and implementation!

[cowtowncoder]

Looks good, merging...