Add execution requirements based on Xcode availability to Swift rules that care about Xcodes.
Add execution requirements based on Xcode availability to Swift rules that care about Xcodes.

This is part of a series of changes to enable Xcode autodetection, but this does not currently change behavior.

RELNOTES: None.
PiperOrigin-RevId: 287349615

bazelbuild/rules_swift,bazelbuild/rules_swift