Let IgxTouchManager pointerDown veto a gesture to avoid blocking scroll

[Copilot]

IgxTouchManager starts tracking on every accepted pointerdown and, via its non-passive touchmove listener, calls preventDefault() while tracking. When attached to document (e.g. Navigation Drawer), this cancels normal page scrolling even when the consumer would ignore the gesture. Addresses the review comments in pullrequestreview-4787557464.

Changes

• core/src/core/touch.ts

  • pointerDown callback signature is now (event: IgxGestureEvent) => boolean | void.
  • When pointerDown returns false, the manager stops tracking immediately via a new _stopTracking() helper — resets _tracking/_panStarted/_pointerId/_startTarget and best-effort releases pointer capture — so touchmove no longer suppresses scrolling for vetoed gestures.

• navigation-drawer/.../navigation-drawer.component.ts

  • panStart (wired as the drawer's pointerDown) now returns boolean: true when a pan is accepted (drawer open, or touch starts within maxEdgeZone), false otherwise (gestures disabled, pinned, non-touch, or touch outside the edge zone), letting the manager bail out and leave scrolling intact.

// touch.ts
if (this.callbacks.pointerDown?.(this._createEvent(event)) === false) {
    this._stopTracking(event.pointerId);
}

Returning nothing preserves the previous behavior, so other consumers are unaffected.