[Java] Add hasNull flag to Vectors

[asfimport]

Add has null flag to Arrow Vector so that for vectors without any null, the null check process should be skipped.

Reporter: Yurui Zhou / @yuruiz

PRs and other links:

• GitHub Pull Request apache/arrow#4199

_{Note: This issue was originally created as ARROW-5198. Please see the migration documentation for further details.}

[asfimport]

Todd Farmer / @toddfarmer:
This issue was last updated over 90 days ago, which may be an indication it is no longer being actively worked. To better reflect the current state, the issue is being unassigned. Please feel free to re-take assignment of the issue if it is being actively worked, or if you plan to start that work soon.