fix: dispatch mouseUp to the widget that received mouseDown

[NemeZZiZZ]

Problem

mouseDownEvent remembers which widget received the press (this._mouseDownWidget = widget, Event.ts:312), but mouseUpEvent ignores it and re-hit-tests at the release position:

mouseUpEvent(e: MouseTouchEvent): boolean {
  const { widget } = this._findWidgetByEvent(e)   // widget under the cursor NOW
  ...
  consumed = widget.dispatchEvent('mouseUpEvent', event)

The mouseup listener lives on documentElement, so releasing outside the chart still reaches this handler — but dispatches to whatever happens to be under the cursor (another pane's widget, an axis, the separator) or to nothing.

Impact

Dragging an overlay point or continuous-drawing with the button released over an axis/separator: the main widget never gets its mouseUpEvent, so OverlayView's mouse-up path (setPressedOverlayInfo({ overlay: null }), forceComplete()) never runs — the overlay stays pressed/unfinished until the next click on the main area.

Fix

Standard mouse-capture semantics: dispatch mouseUpEvent to the widget that received the mouseDownEvent, falling back to the hit-test only when no press is tracked:

const widget = this._mouseDownWidget ?? this._findWidgetByEvent(e).widget

_makeWidgetEvent then also computes event-local coordinates against the widget that actually handles the event, which is correct under capture. _mouseDownWidget was already tracked for the separator-drag path (Event.ts:387); this extends the same semantics to mouse-up.