Increase maximum length of combinator_description, or add max_description_length prototype property

[jagoly]

The combinator description is an extremely convenient place to put settings and information for modded combinators. However, it is unfortunately limited to 499 bytes. If possible, I would like one of two things:

- Increase the character limit for all combinators. Even just going from 499 to 999 would be adequate for my purposes, but if it were possible, twice that again would be preferable.
- Add a new property to CombinatorPrototype, max_description_length, which simply allows you to increase the allowed length for modded combinators. This way no changes would need to be made to the vanilla combinators, if there is some reason for that.

I understand that this is probably quite niche, but it may be the case that increasing the limit amounts to changing a single constant somewhere without any downsides, so I figured I should at least ask