Collapse focus/hover/normal ternaries into Style.controlFill helpers

TextField, NumberField, Dropdown, SearchableDropdown, and Toggle all
painted their background, border color, and border width with the same
three-line ternary ladder (`_focused ? focusFill : _hot ? hoverFill :
normalFill`). Five components × three properties × three branches is a
lot of room for one of them to drift from the others when a new state
ever gets added.

Add controlFill / controlBorder / controlBorderWidth on Style and rewrite
each call site as a single binding. No visual change.

shell/Ui/SearchableDropdown.qml

@@ -109,19 +109,9 @@ Item {
       readonly property bool _focused: trigger.activeFocus
       readonly property bool _hot: triggerHover.hovered || root.hasCursor
 
-      color: trigger._focused
-        ? Style.focusFillFor(root.foreground, root.accent)
-        : (trigger._hot
-          ? Style.hoverFillFor(root.foreground, root.accent)
-          : Style.normalFillFor(root.foreground, root.accent))
-      border.color: trigger._focused
-        ? Style.focusBorderFor(root.foreground, root.accent)
-        : (trigger._hot
-          ? Style.hoverBorderFor(root.foreground, root.accent)
-          : Style.normalBorderFor(root.foreground, root.accent))
-      border.width: trigger._focused
-        ? Style.focusBorderWidth
-        : (trigger._hot ? Style.hoverBorderWidth : Style.normalBorderWidth)
+      color: Style.controlFill(trigger._focused, trigger._hot, root.foreground, root.accent)
+      border.color: Style.controlBorder(trigger._focused, trigger._hot, root.foreground, root.accent)
+      border.width: Style.controlBorderWidth(trigger._focused, trigger._hot)
 
       activeFocusOnTab: true