Support Maven's reproducible build feature for war repackaging

[Jurrie]

Please support reproducible builds for the repackage goal.

This is a follow-up for issue 20176. Previously, the fix for issue 20176 was reverted, and the issue was closed. This was done because the maven-war-plugin did not handle reproducible builds correctly.

Now, I believe the maven-war-plugin is fixed because of MWAR-432 and MWAR-436. The most recent version supports <project.build.outputTimestamp> as far as I can tell.

I commented on issue 20176, but was asked to open up a new one. That would be this one 😀

[wilkinsona]

Just to avoid any confusion, the entire fix for #20176 wasn't reverted, just the war part. It should already be possible to repackage a jar file in a reproducible manner.

[Jurrie]

For reference: the war part was reverted in c4a55a5 on 16-mar-2020.
The Maven WAR plugin was upgraded to 3.3.1 in a35073d on 7-aug-2020.
So, it is probably just a matter of reverting commit c4a55a5.

I'll try to make a pull request for this.

[Jurrie]

I created #25571

[scottfrederick]

Closing in favor of #25571