[7.x] Add dynamic slot name support

[cbl]

This pr adds support for dynamic slot names using the : prefix:

<x-slot :name="$foo">
    {{-- ... --}}
</x-slot>

[driesvints]

@cbl good one!

[mnaderian]

Should we add it to the main docs as Dynamic Slot Names?

[cbl]

@mnabialek I think the way it works now is the way you would expect it to work since dynamic attributes on Blade X components work the same way. However it might be useful to read that it is possible when flying over the docs.