Optimise/add missing calendar[-*] icons/improve metadata

[danielbayley]

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[github-actions]

Added or changed icons

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[ericfennis]

Nice work on optimizing the SVG paths.
Can you describe the use cases for newly added icons?

[danielbayley]

Can you describe the use cases for newly added icons?

@ericfennis Sure, so calendar-[plus/minus]-2 are obviously currently missing variants of https://lucide.dev/icons/calendar-plus and https://lucide.dev/icons/calendar-minus. calendar-slash is date marked/past or busy/future planned event etc… calendar-fold is like next month/look ahead (as if you were to flip to the next page), but can also be bookmark, as folding the corner is an easy way of doing that. Also matches the fold from sticky-note/file etc… (See #1378).

[github-actions]

This PR is stale because it has been open 45 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[ericfennis]

I've removed the calendar-slash icon, the usecase is a bit questionable also since it is proposed in your other icon PRs. We can still add them to the lab branch if you want.