transpile: Factor out more pointer-related functions

[Rua]

This factors out functions for two things: casts involving pointers, and null checking. In the case of == and != operators in a non-conditional context (in operators.rs), this also adds special handling for regular pointers, where only function pointers were specially handled previously. This means that

int b = ptr == NULL;

is now translated with the is_null method as well, instead of with the == operator and core::ptr::null.

[kkysen]

By the way, when you do refactoring PRs like this, can you try to split out the pure moves vs. the semantic changes more carefully/fine-grained? It makes it much harder to review when mostly moves are mixed with some other changes (although I'm not sure if there are better ways of viewing the diffs; I tried --color-moved but it doesn't really work usually).

[Rua]

By the way, when you do refactoring PRs like this, can you try to split out the pure moves vs. the semantic changes more carefully/fine-grained?

How is this now?

[Rua]

Does anything else need to be done here?

[kkysen]

@Rua, I'm going to force push. I need to untangle some commis. The follow-ups I suggested last time need to go in separate commits because they are separate changes, and they're much harder to review when combined into the same commits that are repeatedly rebased.

[kkysen]

@Rua, I split up the latter commits more so that each commit does one thing. Let me know if this looks good. I dropped the last commit, b6c3f64, as I think it's cleaner to make new bindings than have a mutable one here. And I fixed the other comments I had just made earlier.

[Rua]

Yes, looks good.