Add string extensions quote and reverse

[pkwarren]

Add strings.quote and reverse extensions to match Go implementations.

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[pkwarren]

I wasn't sure if these were left out of the string extensions intentionally, but these were two that I saw implemented in cel-go but weren't in cel-java. The third one format is much more complex so I didn't tackle that one.

[l46kok]

I wasn't sure if these were left out of the string extensions intentionally, but these were two that I saw implemented in cel-go but weren't in cel-java. The third one format is much more complex so I didn't tackle that one.

Thanks for the contribution. This was just work we hadn't been able to get to, and should definitely be added in CEL-Java.

I'll review more thoroughly soon but in the meanwhile -- would you mind enabling the conformance tests for strings.quote by removing these lines:

https://github.com/google/cel-java/blob/main/conformance/src/test/java/dev/cel/conformance/BUILD.bazel#L123
https://github.com/google/cel-java/blob/main/conformance/src/test/java/dev/cel/conformance/BUILD.bazel#L152

[pkwarren]

Enabled strings.quote in conformance tests in 6207811.

[l46kok]

Please add the newly added function to the documentation: https://github.com/google/cel-java/blob/main/extensions/src/main/java/dev/cel/extensions/README.md?plain=1#L388

You should be able to copy the relevant sections from go's README: https://github.com/google/cel-go/blob/master/ext/README.md

[pkwarren]

Thanks for the thorough review. I believe I've addressed the feedback - only question is on #998 (comment).

[l46kok]

LGTM -- just a few nits