Add types to NumberParseException

[BenMorel]

No description provided.

[BenMorel]

@giggsey Would you be open to another PR adding strong types to properties, parameters, return types throughout the codebase? The codebase can be modernized quite a lot, while keeping compatibility with PHP 7.4.

[giggsey]

Thanks.

I think adding stronger types will be fine for @internal classes, or private properties. Anything else would be a BC break, which I'm not keen on.

libphonenumber-for-php-lite has the stronger types from the more modern PHP.

[BenMorel]

I understand, matching Google's releases implies not being able to break things whenever you want. If Google ever releases a v9, maybe it'll be an opportunity to perform this upgrade!