ICU-22549 Add fuzzer for NumberFormatter

[FrankYFTang]

Checklist

• Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-22549
• Required: The PR title must be prefixed with a JIRA Issue number.
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• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

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[richgillam]

This looks okay to me, I think, but I'd like @sffc or somebody else more familiar with NumberFormatter to weigh in on whether there are additional APIs on this class you should be fuzzing.

[sffc]

Suggestion: take 4 bytes of the input and make them into a floating point number to be formatted. Parsing the skeleton is good, but we can also cover data loading. However, doing so will make the fuzzer a bit slower.

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• icu4c/source/test/fuzzer/Makefile.in is different
• icu4c/source/test/fuzzer/number_formatter_fuzzer.cpp is different

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[FrankYFTang]

Suggestion: take 4 bytes of the input and make them into a floating point number to be formatted. Parsing the skeleton is good, but we can also cover data loading. However, doing so will make the fuzzer a bit slower.

I implemented it now. PTAL

[richgillam]

I like it. Hopefully Shane does too.

[sffc]

Looks right; it's possible I missed something in all the pointer math