[Java] Resolve problems of DecimalVector APIs on ArrowBufs

[asfimport]

Unlike other fixed width vectors, DecimalVectors have some APIs that directly manipulate an ArrowBuf (e.g. `void set(int index, int isSet, int start, ArrowBuf buffer)`).

After supporting 64-bit ArrowBufs, we need to adjust such APIs so that they work properly. 

Reporter: Liya Fan / @liyafan82
Assignee: Liya Fan / @liyafan82

PRs and other links:

• GitHub Pull Request #8455

_{Note: This issue was originally created as ARROW-10294. Please see the migration documentation for further details.}

[asfimport]

Micah Kornfield / @emkornfield:
Issue resolved by pull request 8455
#8455