Java 12-17API additions

[zbynek]

Fixes #9872
Fixes #10091
Fixes #9991

[niloc132]

Nice work on the draft - some quick feedback

[niloc132]

please also include a set of these tests that does not do a hideFromCompiler, so we can make sure that if the compiler is able to constant-fold these method calls, that it does so correctly.

[zbynek]

I did not implement any tests without hideFromCompiler yet since I wasn't sure which methods need them. It seems that tests either hide all inputs from compiler (like the ones from https://github.com/gwtproject/gwt/pull/9975/files#diff-79013db0b72ddfb9522327d93e6c5804f44c160025590e971ddfc7fd4eb7c045R26 ) or hide nothing (https://github.com/zbynek/gwt/blob/f0c1486a46018aec9de93458136cfc161f569e81/user/test/com/google/gwt/emultest/java/lang/StringTest.java#L542 ). Also I'm not sure if it wouldn't be better to test the constant-folding optimization and verify that these are actually folded rather than make assertions where we don't know if we're testing folding or emulation.

[niloc132]

Using hideFromCompiler ensures that the emulated sources provided can be called and function the way that the test expects. Passing a constant and allowing constant folding means that the operation will be performed by the compiler itself, using the JRE's own implementation, which does two things for us: we know that constant folding doesn't somehow break with this call, and that the JRE implementation doesn't behave in a way that fails the test.

This isn't a guarantee - the constant folding mechanism is pretty specific (I've been meaning to file a bug about that) and won't always kick in, but it does let us get a little more coverage.

[zbynek]

Full build https://github.com/zbynek/gwt/actions/runs/14282864925

[niloc132]

I think this should have a handful of more tests too:

• " x\n. " to confirm that the second line is entirely removed
• " x\n\n y" to confirm blank lines do not have their indent counted
• ...except the last line, where a blank line's indent is meaningful. Combining the above two notes, something like " x\n " should yield " x\n" (and " x\n " should have the same result)

https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/String.html#stripIndent()