[6.x] Add inputs to edit focal points

[jackmcdade]

References statamic/ideas#628

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Note

Low Risk
UI-only change in the focal point editor that mainly adds input controls and value validation/clamping, with minimal impact beyond stored focal point formatting.

Overview
Adds numeric ui-input fields to directly edit focal point x/y percentages and z zoom, alongside the existing click-to-set and zoom slider controls.

Normalizes focal point values to numbers and introduces clamping/rounding (clampPercent, clampZoom) applied on mount, manual input changes, image clicks, and before emitting selected, preventing invalid or out-of-range coordinates/zoom from being saved.

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