build: enable error-prone's FormatString check

[rmuir]

This check will find some printf-style format problems at compile-time instead of runtime: enable it.

Please note: this won't find my original bug yet on #14901, maybe because the file is in src/java24. But I tested it works by adding an extra %s to a format string in IndexWriter.java and it properly fails the build. I will dig on the src/java24 issue separately... I suspect we're not running error-prone on these sources.

We have hundreds of such format strings in the codebase, many of which might not have perfect test coverage (they are printing), so it is a good check to have.

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[uschindler]

I think we can backport this.

[rmuir]

@uschindler It is a good idea. I will take care of it shortly.

[rmuir]

Sorry: I came back to this and its conflict-central because build sources are moved around. I'm gonna stay focused on improving main, but of course don't mind if anyone wants to backport PRs of interest.

[dweiss]

The build on main is far from branch_10x. I've been wondering if backporting everything is a good idea and when to do it (now, later). I have a feeling that - until main reaches some kind of maturity - backporting will involve a lot of extra work. Maybe we should hold off and do it as a one-step later, don't know.

[rmuir]

it is also ok to make new major releases when there is lots of change like this :)