[Feature] Add practical field aggregators available in Java Paimon

[liangjie3138]

Search before asking

• I searched in the issues and found nothing similar.

Motivation

Complete the Paimon C++ SDK with practical field aggregators that are already supported by Java Paimon.

Solution

Add support for the following field aggregators:

• collect
• merge_map
• nested_update
• rbm64
• hll_sketch
• theta_sketch

Anything else?

No response

Are you willing to submit a PR?

• I'm willing to submit a PR!

[lxy-9602]

Thanks a lot for raising this issue! If you’re interested in submitting a PR for it, we’d be more than happy to review and merge it.