[Java] Remove value boxing/unboxing for ApproxEqualsVisitor

[asfimport]

As discussed in #5195 (comment), there are some problems with the current ways of comparing floating point vectors, we solve them in this PR:

1. there are if statements/duplicated members in ApproxEqualsVisitor, making the code redundant and less clear.
2. the comparion of float4 and float8 are based on wrapped objects Float and Double, which may have performance penalty.

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

PRs and other links:

• GitHub Pull Request #5304

_{Note: This issue was originally created as ARROW-6458. Please see the migration documentation for further details.}

[asfimport]

Micah Kornfield / @emkornfield:
Issue resolved by pull request 5304
#5304