implementation of pinch gestures

[kefaslungu]

Link to issue number:

#19938

Summary of the issue:

This PR adds pinch in and pinch out gestures as the first step toward expanding NVDA's touch gestures. See #19938 for more information.

Description of user facing changes:

Two new touch gestures are now available for assignment:

• Pinch in: place two fingers on the screen and move them toward each other.
• Pinch out: place two fingers on the screen and move them away from each other.

The fingers must move at least 50 pixels closer together or further apart to be recognised as a pinch.

Description of developer facing changes:

Description of development approach:

The pinch gesture is detected entirely within TrackerManager in touchTracker.py.
When two fingers are on screen simultaneously, the initial distance between them is recorded.
When both fingers lift, the final distance is computed from their last known positions.
If the change in distance meets or exceeds the minimum threshold, a pinch in or pinch out MultiTouchTracker is queued and emitted like any other gesture.

Testing strategy:

To test, you must have a touch environment, and must be able to:

• Build from source and
• self sign the build.
  Or get the snapshot

1. Build NVDA from the pinchgestures branch and enable touch interaction support.
2. Turn on input help mode (NVDA+1).
3. Place two fingers on the screen and move them toward each other — NVDA should announce "2 finger pinch in".
4. Place two fingers on the screen and move them away from each other — NVDA should announce "2 finger pinch out".
5. Assign a script to each gesture via the Input Gestures dialog and confirm the script executes correctly.
6. Verify that single-finger gestures are unaffected.
7. Verify that a two-finger tap is still recognised correctly and not confused with a pinch.

Known issues with pull request:

None.

Code Review Checklist:

• Documentation:
  • Change log entry
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• API is compatible with existing add-ons.
• Security precautions taken.