Add opt-in Jackson Blackbird optimization to ObjectMappers

[parker89]

Adds opt-in Jackson Blackbird support to ObjectMappers (off by default). ObjectMapperOptimizations.createModules(boolean) plus new server/client mapper overloads register BlackbirdModule only when explicitly requested.

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Description

Add opt-in Jackson Blackbird optimization to ObjectMappers

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[mpritham]

Did you have other optimizations in mind down the line?

I wonder if we should name this something like "newSingleInstantiatedServerSmileMapper" or something to make it clear that this should not be called multiple times, and then enable blackbird by default for this case.

Maybe we can write an errorprone check(? e.g. only created in a final variable in a class - though this is a bit restrictive)

[bjlaub]

I think a big issue I have with this change is that it is not obvious that calling ObjectMappers.new*Mapper(true) should be done with great care due to FasterXML/jackson-modules-base#147.

We have quite a bit of code internally that uses this pattern; existing code won't be affected (which is good), but new code can very easily be written in a way that causes the leak. Using a memoization approach might be better, with a separate API that makes it very obvious that you are getting a shared ObjectMapper, not a new one.