[Java/Python] Add unit test for pyarrow.decimal128 in Array.from_jvm

[asfimport]

Follow-up after #18209. We need to find the correct code to construct Java decimals and fill them into a DecimalVector. Afterwards, we should activate the decimal128 type on test_jvm_array and ensure that we load them correctly from Java into Python.

Reporter: Uwe Korn / @xhochy

Related issues:

• [Java/Python] in-process vector sharing from Java to Python (is a child of)

_{Note: This issue was originally created as ARROW-2606. Please see the migration documentation for further details.}

[asfimport]

Aravind R Yarram:
@xhochy I'd like to contribute. I have good experience on Java, Scala, BigData and related ecosystem. However, I could use some help to get started. i.e. setting up the dev env etc. I was looking the GitHub project Readme page but couldn't find any details.

[asfimport]

Uwe Korn / @xhochy:
[~aravind.yarram] Have a look at https://arrow.apache.org/docs/python/development.html

[asfimport]

Aravind R Yarram:
@xhochy thanks. looking into it