c-select: Add more powerful control around the menu item slot

[ascott18]

This will provide more flexibility to users on how they want the contents of the list item to be displayed. Opens up the ability to add other prepend/append content or other parts of v-list-item without having to resort to wonky CSS.

Move the v-list-item-title to only wrap around the item slot, which is a slot that is intended to contain relatively pure CSS since it is also shown as the selections for the control.

[ascott18]

I'm not convinced the breakage is worth it here. Will wait until specific needs arise and then make changes to address those needs.

Just moving the slot up to not include the -title won't immediately fix all issues here since prepend/append are done through slots on v-list-item, so those would have to be passed through as well somehow. Might end up needing to be a whole new slot that must produce a whole v-list-item. (more similar to existing vuetify dropdowns).