Fixup Apple target's description strings

[BlackHoleFox]

Noticed this inconsistency in how the Apple target's had their new descriptions written while looking at #130614, and figured it was easy enough to fixup shortly. I think prefixing every OS with Apple is clearer, especially for less known ones like visionOS and watchOS; so that's what was done here along with making the architecture names more consistent and then some other small tweaks.

r​? @thomcc

cc @madsmtm

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r? @cjgillot

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[rustbot]

These commits modify compiler targets.
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[jieyouxu]

Thanks, this seems nice for consistency, I'll delegate the approval to @madsmtm, so please r=me if the renames make sense to you @madsmtm :)

[jieyouxu]

@bors rollup

[jieyouxu]

@bors delegate=@madsmtm

[bors]

✌️ @madsmtm, you can now approve this pull request!

If @jieyouxu told you to "r=me" after making some further change, please make that change, then do @bors r=@jieyouxu

[madsmtm]

Don't have much opinion on this, looks good other than the Mac Catalyst thing noted