add jackson 3 migration note about JsonParser.readValuesAs and what to use instead

[pjfanning]

• see Jackson 3: JsonParser.readAsValues gone - what to use instead? jackson-core#1485
• there might be more methods like this in jackson-core 2.x that used ObjectCodec that were also removed

[cowtowncoder]

On point 2: anything that used ObjectCodec should now use one of ObjectReadContext (parser) / ObjectWriteContext (generator) so no methods should have been removed due to removal of ObjectCodec itself.

... except for multi-value reads that ObjectReadContext does not support. So that is the reason here.
I added Javadoc note in 2.20 branch for upcoming removal: should not deprecate as it's still valid for 2.x (I think).

But there is now strong recommendation of creating parsers and generators through ObjectMapper instead of directly via JsonFactory -- former will properly connect ObjectReadContext / ObjectWriteContext; latter will require caller to pass (and methods that do not take context are deprecated).

[modular-music-and-code]

Thanks to all for the replies. I isolated a use case where i prove that Jackson-3 has a regression for streaming with ObjectReader.readValues

[cowtowncoder]

Issues reported have been resolved, closing.