This commit moves the gradle wrapper jar file to a hidden directory, so
that it does not clutter the top level names seen when doing an ls in
the project. The actual jar file is never manually edited, and only
changed by running `./gradlew wrapper ...` so it is not important for
this directory to be "visible".
We have agreed to introduce the Gradle wrapper to simplify workflows for
developers, and managing infrastructure (e.g., CI, release builds, etc.)
as well as consideration for the fact that other projects in our stack
use Gradle and do not necessarily want to be tied to our Gradle version.
Relates #28065
Ryan Ernst
Jason Tedor
Shay Banon