Restrict let_and_return if the let binding is large

Currently, the let_and_return lint is always triggered. I have quite a lot of code which looks like:

let something = match something_else {
    Variant1 => { /* something */},
    ...
    Variant_some_very_large_number => { /* whatever */ }
};

something

Here, I believe it is a lot clearer to explicitly have the let binding, since you may have to scroll quite far to see that there's no semi-colon at the end of the match block for it to be obvious that it's the return expression. I don't know what a suitable size threshold would be, or even if it's possible to reasonably make restrictions based on that.

Of course, I'm open to other ways of writing code blocks like this which would also solve the issue!

Start at the let_and_return lint entry point and inspect how it identifies the return expression. Review the discussion around a size threshold or alternative rule, then determine whether the large match-binding case can be distinguished reliably; done means the behavior and threshold are covered by focused lint tests.