Rust: Type inference for `for` loops and array expressions

[geoffw0]

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Adds type inference for for loops and array expressions. Currently for for loops this is limited to loops iterating through arrays.

@hvitved please advise.

• I think for the more general cases we will need to decode the Iterator type and perhaps understand IntoIterator.
• I'm not sure whether I should be attempting to model implicit dereferences, or perhaps a more general solution for that problem might be in the works?

[geoffw0]

@hvitved do you think this is heading in the right direction?

[geoffw0]

Ready for review: there are gaps (and apparently a conflict with main), but we get some useful results and I'd like to push towards merging this ASAP.

[geoffw0]

:tada: