Bug: There is no error/warning if you use two <<else>>'s in the same <<if>> statement about twee3-language-tools

[cyrusfirheir]

Child macros and their position and stuff aren't validated as of now. Currently, the parser only sees the entire if block, and not different sections inside it.

[MinusGix]

We might be able to do this:

• Get the range for the if macro we're looking at
• Iterate over all macros (starting after current). Filter so that their start is within the if macros range.
• For each of those macros, if they're a container macro then we filter out all the macros within its range, this avoids checking the macros inside the container which would be bad
• If it is one of our children macros then we keep a count of it (probably only for ones with max field defined on them, where we need to do that)
• If it goes over the max field (we could also easily add a min, but I'm unsure if there's any which would benefit from that?) then we warn.

It is a bit more expensive to compute than I'd like, but avoids generating an entire tree since we don't need it. I'll try implementing this.
It would allow for a min requirement, as well as requirements like else must always be after either nothing (if) or elseif (though this one is a bit more complex).