sql/types: do not panic formatting unhydrated UDTs

[ajwerner]

Before this patch, if a bug resulted in a UDT's types.T getting to a point where it was being formatted to a string without being hydrated, a panic would occur. Now the type is formatted into an OIDTypeReference which is slightly less pretty, but is valid.

Relates to #85447

Release note: None

[cockroach-teamcity]

This change is 

[ajwerner]

TFTR!

bors r+

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