pf: Update PF3→PF4 style overrides
pf: Update PF3→PF4 style overrides

- Add missing comment
- Fix regression for btn-primary hovering
- Stretch dropdown menus to the dropdowns
- Properly space expand/collapse separator

For Composer:
- Fix selected items on dropdowns
- Rebase icon size on PF4's rem size

Closes #12253
Addresses #12210

deryni/cockpit,cockpit-project/cockpit,deryni/cockpit,cockpituous/cockpit,mvollmer/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,garrett/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,garrett/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,deryni/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,garrett/cockpit,martinpitt/cockpit,cockpit-project/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpituous/cockpit,deryni/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,garrett/cockpit,mvollmer/cockpit,mvollmer/cockpit,deryni/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,garrett/cockpit,deryni/cockpit,cockpit-project/cockpit,cockpituous/cockpit,deryni/cockpit