fix(java): Move schema caching to unsafe trait to avoid issues when using non-inferred schema.

[wywen]

What does this PR do?

This PR removes the java specific ExtField class from the schema and moves the extData mechanism to the internal UnsafeTrait class. This is necessary because ExtField is only created internally from inferSchema method used by java, and we would potentially import or derive schemas from other sources (e.g XLANG, handwritten schema, arrow-native source) -- those schemas will be incompatible when we attempt to retrieve the cached schema. Removing schema-caching will fix the issue, but create allocations, so after some discussion, we decided to move the mechanism to the internal UnsafeTrait class.

This implementation makes changes internal API:

• Derived classes from UnsafeTrait need to initialize the extData cache and define the number of extData slots needed.
• The internal getStruct method needs to define which slot we use to retrieve extData.

Other:

• REVERTED: pom.xml for fury-format will automatically run tests with appropriate --add-opens flag for arrow

Related issues

Does this PR introduce any user-facing change?

N/A

• Does this PR introduce any public API change?
• Does this PR introduce any binary protocol compatibility change?

Benchmark

[chaokunyang]

LGTM