ICU-22568 return TimeZomeFormat::createInstance for bogus locale

[FrankYFTang]

Use local UErrorCode and proper error handling to continue the TimeZomeFormat::createInstance when the locale is bogus.

Checklist

• Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-22568
• Required: The PR title must be prefixed with a JIRA Issue number.
• Required: The PR description must include the link to the Jira Issue, for example by completing the URL in the first checklist item
• Required: Each commit message must be prefixed with a JIRA Issue number.
• Issue accepted (done by Technical Committee after discussion)
• Tests included, if applicable
• API docs and/or User Guide docs changed or added, if applicable

[FrankYFTang]

@markusicu friendly ping

[richgillam]

The code looks fine, but I'm a little unclear-- you now get back a valid TimeZoneFormat when you pass in a bogus locale ID, but what does it do, and what locale is it using? Does it always throw error, or is it just an ordinary TimeZoneFormat based on the root locale? Or something else?