[Java] Use Fully Qualified Name for java.util.Locale in Generated Classes

[Chrimle]

Fixes #22313 and fixes #22269, by doing a partial revert of #21871, and replacing all introduced import java.util.Locale; with Fully-Qualified uses i.e. java.util.Locale. The reason is that the import of java.util.Locale will clash/conflict with any other class named Locale in the current package. The intention is to again allow custom classes, pojos/enums, to be named Locale and to be used in other generated classes, as it was pre-v7.16.0.

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[Chrimle]

@wing328 really not sure why it is failing. The error indicates that the samples are not updated, but they are 🤔

Edit: nevermind, the /bin structure is unlike the /resources structure, so had so also re-run "spring*" 🤦

[Picazsoo]

Hello @Chrimle, I am not a maintainer, but this change looks sensible to me. I really like that you changed it everywhere even though it might theoretically not cause an issue everywhere, since I expect others can be expected to follow the style going forward when submitting a PR.

As is, I am afraid that someone might unknowingly reintroduce this bug with good intentions. Maybe at least a unit test with api spec testing for the absence of import java.util.Locale and presence of the FQN would make sense? But I understand testing it everywhere would be pretty excessive. But anything is better than nothing in my opinion.

[Chrimle]

@Picazsoo Correction; Initially ALL imports were replaced by inline:ing. However, on second thought, it was deemed a bit risky, since it would affect non-pojo classes. Hence, it was reverted, and only the mustache-files modified in #21871 , were partially reverted (removing the imports) and the usage of Locales are now fully qualified.

This means, classes pre-7.16.0 that were importing Locale have NOT been modified. Only the mustache files, and the resulting generated pojos, modified in 7.16.0.

Edit: Should the PR title be reworded to better reflect this? Suggestions welcomed