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ARROW-5250: [Java] Add javadoc comments to public methods, remove style check suppression.

Apologies for the large CL.  After this the one last large javadoc fixing of 2019 is to enable checkstyle to types as well and add missing docs to those.

If possible my review preference would be as suggested edits if at all possible but any feedback is welcome.

In addition to javadocs, I also added private constructors to classes containing only static utility methods.

For a small set of test methods I converted them to "private" instead of providing javadocs.

The approach taken was to provide minimal useful javadoc and not necessarily completely formatted with all parameters, etc.  The intent is to enable style checking to "stop" the bleeding so patch authors can provide useful documentation for new API methods going forward.

Author: Micah Kornfield <emkornfield@gmail.com>

Closes #4243 from emkornfield/java_docs and squashes the following commits:

fa1e15b9 <Micah Kornfield> Add missing doc to duration
b230e36c <Micah Kornfield> Address code review comments and fix some other small style issues on self review
da6afad7 <Micah Kornfield> fix one more typo
6ee017d6 <Micah Kornfield> Supress load errors.
1fe41b7b <Micah Kornfield> Add comments to changes on master
5cd69077 <Micah Kornfield> address code review comments fix some sentence styles
5e2e52f6 <Micah Kornfield> Javadoc without tests
23d7acaa <Micah Kornfield> code changes