Add return type extension for normalize_whitespace

[IanDelMar]

Adds return type extension for normalize_whitespace().

For constant strings:

• trims strings
• keeps empty and falsy strings
• generalises all other constant strings

For non-constant strings:

• converts non-falsy-string to non-empty-string (' 0' is no longer non-falsy after trim())
• converts non-empty-string to string (' ' is no longer non-empty after trim())
• preserves all other AccessoryTypes

[IanDelMar]

The error is related to uppercase-string, introduced in PHPStan 1.12.12. It appears some issues around it were only resolved in 2.0.3. Should we remove the ' FOO ' assertion, or bump the minimum required PHPStan version to 2.0.3? I think we can safely just remove the assertion.

[IanDelMar]

Perhaps uppercase-string was introduced in v1 and not in v2 initially. From the release description of version 2.0.3:

This release includes improvements and fixes from PHPStan 1.12.12.

Still, we can just remove the assertion. The type is not actively used, but is part of the return types composed from the AccessoryTypes by PHPStan.

[szepeviktor]

🫡 abnormalize_whitespace