Skip maven module formatting if module has not changed since last formatting

[fabiencelier]

Describe the bug We have a large Java project with more than 100 maven modules. When we apply the formatter it triggers on all the modules, which takes a long time (more than 2 minutes)

Expected behavior We would like to have an option to skip the modules if it unchanged since last formatting. This could be done form instance by taking a checksum of all the files to format, store this checksum, then check if the checksum has changed before starting to format.

This would greatly help us as we generally only work on a few modules at a time and don't need to apply the formatter again and again on all the files.