Mixin cleanup part 2

[modmuss50]

Part 2 of cherry picking @Earthcomputer 's PR: #5118

Part 3 I will look at the comments on the orginal PR regarding removing unneeded locals, lets keep it focused and merge this one quickly to reduce conflicts.

[LlamaLad7]

Personally I'm not entirely convinced, see my comments from the original PR:

• Using names for argsOnly locals seems to me less stable than using ordinals / implicits, since it seems more likely for the internal code to change than the external api
• Implicit mode seems potentially more stable than names when possible for normal locals, though I feel less strongly about this

If people have reason to disagree then we can discuss but I don't think "use name everywhere" is a sensible blanket strategy.
I suggested avoiding the locals where possible because that's definitely better, whereas a lot of these changes are dubiously better.

[modmuss50]

Ah sorry, I must have missed that comment on the other PR.

Good point on argsOnly, I think I will change that.

I dont think stability across versions is the main goal here if something is renamed/chages its usually done for a reason, and more than likely may cause the mixin to behave differently.