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GH-38614: [Java] Add VarBinary and VarCharWriter helper methods to more writers (#38631)

### Rationale for this change
Add the overrides for new convenience Writer methods added to VarCharWriter and VarBinaryWriter so that classes that
use composition such as UnionWriter and PromotableWriter can invoke them properly.

### What changes are included in this PR?
- Rename from writeTo$type to write$type for consistency with other methods
- Add new helper methods to PromotableWriter
- Add new helper methods to complex writers such as list and union

### Are these changes tested?
Yes. New unit tests added for several Writer classes.

 **This PR includes breaking changes to public APIs.** 
The writeTo<Type>() and similar methods in Writers have been renamed to just write<Type>()

* Closes: #38614

Authored-by: James Duong <james.duong@improving.com>
Signed-off-by: David Li <li.davidm96@gmail.com>