[WC-3522] fix RTL label alignment for control-label/checkbox/radio

[yordan-st]

Summary

• Labels misaligned in RTL (Arabic) — regression, previously fixed in Atlas Core 3.18.0.
• Root cause: WC-2936's fix (removed text-align: left on .control-label) was silently reverted by a later, unrelated "form edit styling fix" commit. Checkbox/radio label gutters never had RTL support after the Atlas 4 rewrite dropped legacy bootstrap-rtl handling.
• Switched to logical CSS properties (text-align: start, margin-inline-start, padding-inline-end) in _input.scss, _check-box.scss, _radio-button.scss so RTL works without separate [dir=rtl] overrides.

Test plan

• Verified via headless computed-style check (compiled CSS + dir="rtl" fixture): .control-label text-align resolves to logical start, checkbox/radio label gutter moves from margin-left to margin-right under RTL.
• Manual check in Studio Pro with Arabic locale on a form with labels + checkboxes + radio buttons.
• Confirm no visual regression in LTR (English) — logical properties should be no-ops there.

Ticket: WC-3522