Enhance `needless_collect` to cover ".join"

[profetia]

Description

When having an iterator of strings, one might use .collect<Vec<_>>().join(" ") to concat the strings with a given seperator. However, it might be better to use .intersperse then .collect directly, if the intersperse feature is enabled. For example

let v = vec!["123"];
let iter = v.into_iter();
iter.collect::<Vec<_>>().join(",");

Use instead:

let v = vec!["123"];
let iter = v.into_iter();
iter.intersperse(",").collect::<String>();

Version

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