Condition cleanup

[Nicofisi]

Copy-pasted from the message of the first commit (only reformatted line endings):

• changed some conditions to property conditions, where it made sense
• replaced new Checker() { ... } with lambdas
• utilized the static toString method of the PropertyCondition class in a few non-property conditions where it made sense, for guaranteed toString consistency and proper grammar
• in nested Expression#check calls, put the negation in the outer call, because this way it makes more sense logically. For some 'proof', see the CondCompare class written by Njol, it has always had the the isNegated() parameter only in the outer call. I've considered this deeply myself too and I am greatly convicted it makes more sense this way
• changed the method order in a few classes
• fixed up the nullability annotations in a few classes
• added tabs on empty lines in some files where they were missing (we plan to remove them afaik, but for now for consistency)
• added or removed empty lines in a few places, for consistency and readability
• suppressed a deprecation warning in one place where it was clear that we're aware that the method was deprecated although we still need to use it to support older Minecraft versions
• added assert false;s before return false;s that should never be run

[Nicofisi]

Long story short: the 'fetch' button in the official GitHub Desktop app is for some reason broken and it pushed the commits to master instead... feel free to make comments about any aspect of the commits and I will reply to all of them or even revert the whole thing if necessary... "thanks GitHub", and sorry again to everyone

[bensku]

How stable is this?

[Nicofisi]

I've read all the changes line be line three times before committing, and 99% of them were just simple reformats or condition -> property condition updates, so I'm quite confident this should be stable... I'll build a jar and ask a few people to confirm the whole thing in action in real scripts ASAP though, and will report back either today or the day after tomorrow