Make lifetime elision help more useful on type signatures.

[crhino]

Fixes #19707.

In terms of output, it currently uses the form argument #1, argument #2, etc. If anyone has any better suggestions I would be glad to consider them.

[rust-highfive]

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[nrc]

Looks good! For the output I think there should only be backticks around the name of the argument if it is the actual name. If it is "argument #1" or whatever, then there shouldn't be backticks.

Also, I would just use "argument 1" instead of "argument #1" because the user might wonder if the # has any special meaning (and indeed in future Rust it might have some special meaning), otherwise it is a good choice of output.

[nrc]

nit: please add spaces around the -> and after the first :

[crhino]

That all makes sense to me, addressed in the commit above.

[nrc]

It would be more idiomatic Rust to re-assign to name and make it immutable (i.e., remove mut and add let name = ...

[crhino]

Done. Should I rebase and squash?

[nrc]

You don't actually need to change the name to help_name, just keeping name is fine, but either way works for me

[nrc]

@crhino yes please, r=me when you do

[crhino]

It felt a little weird to keep the name as name, I wanted something that told me I was making it more user friendly.

r=nick29581