[BUG] No validation of format strings when formatting dates in legacy timeParserPolicy mode

[andygrove]

Describe the bug
PR #2875 added support for LEGACY timeParserPolicy when parsing strings to temporal types but it also inadvertently enabled LEGACY timeParserPolicy for formatting dates as strings. This works fine for many format strings but could potentially produce wrong results for format strings that have a different meaning between LEGACY and CORRECTED mode.

Steps/Code to reproduce bug
I haven't tried to reproduce the bug yet. This issue is to track the work of doing that.

Expected behavior
If the user provides a format string in LEGACY mode that has a different meaning in CORRECTED mode we should either throw an error or produce the correct results.

Environment details (please complete the following information)
N/A

Additional context
N/A

[andygrove]

I was wrong about this. The base class UnixTimeExprMeta does check that we support the format both for parsing and formatting. No further action is required.