Rename iter::Iterator::intersperse() to ::separate()

[lukaslueg]

Following up in the suggestion voiced here, this

• renames Iterator::intersperse() to Iterator::separate()
• adds a doc-alias "intersperse" on separate()
• renames Iterator::intersperse_with() to Iterator::separate_with()
• renames the associated structs and modules, and updates all references

in order to move on wrt #79524. I have no opinion wrt #79524 (comment) being the correct solution to solve #79524

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[rustbot]

Some changes occurred in src/tools/clippy

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HIR ty lowering was modified

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Some changes occurred in src/librustdoc/clean/types.rs

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[joboet]

r? libs-api

[camelid]

Just wanted to note that there was some disagreement in the associated issue about whether we should merge separate and separate_with into one method separate that takes a closure. I'm personally in favor of two separate methods since this is the usual design in Rust and since a constant separator is much more common. But others disagree so that should be decided before merging this PR.

[bors]

☔ The latest upstream changes (presumably #123396) made this pull request unmergeable. Please resolve the merge conflicts.

[jadebenn]

Not to bikeshed too much, but I think separate is an awfully non-descriptive name for what this method does. My intuition at seeing that name would be that it somehow breaks up an existing collection, not that it adds a new element between each instance.

Something along the lines of interject, interleave, interweave, interlace, or perhaps even justseparator would seem more descriptive to me if the name just needs to be changed to avoid a conflict with itertools.

[Amanieu]

To give an update, we're currently trying to work around the naming conflict with a language-level feature: #89151 (comment)