Use char and latin1 singletons in deepfreeze

[oraluben]

Feature or enhancement

Since #32152, deepfreeze will try to use static string singletons if possible.
But chars and latin1 singletons are not used. Here I propose to reuse them as well.

Pitch

Previous discussion

Linked PRs

• gh-103875: Use char and latin1 singletons in deepfreeze. #103876