Simple mapping optimization fixes

[brianrourkeboll]

Description

Followup to #16832, #16948, #17067, etc.

Fixes #17708.

• Evaluate expr exactly once in [|for … in expr -> …|] when expr is an array.
• Don't rebind the loop variable or read from the source array when the loop variable is unused in the loop body in, e.g., [|for _ in expr -> …|] when expr is an array. There is no need to emit a ldelem from expr and rebind it to the loop variable in this case since the loop variable is never used.
• Handle more complex patterns for pat in [|for pat in … -> …|], [for pat in … -> …].

Checklist

• Test cases added.
• Release notes entry updated.

Notes

The diff for LowerComputedCollections.fs will be smaller if you view the diff with whitespace changes hidden.

Things to look for in the baseline diffs:

• The array expression in something like [|for … in expr -> …|] when expr is an array should be present/evaluated exactly once (and bound to a local using stloc).
• When pat is not used in the loop body in [|for pat in expr -> …|] (e.g., when pat is _) and expr is an array, there should be no ldelem that reads from the source array.
• The optimizations should be applied even when pat in [|for pat in … -> …|], [for pat in … -> …] is something more complex than a named pattern or a wildcard.

[github-actions]

❗ Release notes required

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✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/9.0.100.md

[vzarytovskii]

Thanks for the quick fix!