Small: Optimize `suspicious_xor_used_as_pow`

[blyxyas]

The suspicious_xor_used_as_pow lint is very poorly done (it was my first lint ❤️!), this lines in particular, instead of getting the context, it takes a snippet of the code. It's horrible.

If someone could fix it, it would improve a lot that lint's performance!

cc @Centri3 Maybe interesting for you?

[Centri3]

Hmm I'll take a look. I'm a bit curious on instead of getting the context, unless I'm missing something, NumericLiteral requires a snippet...

This could probably be rewritten to just use the LitKind, though, at the cost of less abstraction

[blyxyas]

Sorry for the brain melt:
I meant that instead of checking a snippet (which is really slow), just get the typeck results and parse them.

[Centri3]

Hmm, is even that necessary? Is there any reason it can't use the LitKind? I don't think Ty has any extra info regarding whether it's a decimal or not, so at the end of day I believe a snippet will likely be needed regardless.

[blyxyas]

@rustbot claim