ICU-22929 Improve fuzzer to find leak from udat_open

[FrankYFTang]

Try to find out what cause ICU-23008. Use ICU-22929 as bug number to improve fuzzer to find the problem.
According to ICU-23008 bug report, the leak of DecimalFormatSymbols can be reach by udat_open when the style is UDAT_PATTERN

Checklist

• Required: Issue filed: ICU-22929
• Required: The PR title must be prefixed with a JIRA Issue number. Example: "ICU-1234 Fix xyz"
• Required: Each commit message must be prefixed with a JIRA Issue number. Example: "ICU-1234 Fix xyz"
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

[richgillam]

LGTM.

[cjchapman]

Thanks for adding this!