Refactor: Use borrowed types for arguments

[danielsn]

Description of changes:

As per https://rust-unofficial.github.io/patterns/idioms/coercion-arguments.html#use-borrowed-types-for-arguments we should prefer &[T] to &Vec<T> for function arguments. Doing so

Resolved issues:

Initial step on #270

Call-outs:

Testing:

• How is this change tested? Existing tests

• Is this a refactor change? Yes

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[avanhatt]

LGTM

[avanhatt]

Actually, should we be doing this change for &mut Vec<T> args too?

[danielsn]

Actually, should we be doing this change for &mut Vec<T> args too?

220 |                         fargs.push(index_param);
    |                               ^^^^ method not found in `&mut [expr::Expr]`