Reland: Trackpad gesture PointerData types

[moffatman]

Original PR was #28571
Reverted in #31375
Should be acceptable now thanks to flutter/flutter#98202

This commit adds support to the engine core for encoding trackpad gestures for to the framework. This covers zoom, rotate, and pan gestures. The changes to send trackpad gestures from each platform will come in follow-up PRs.

1. New types of PointerChange: panZoomStart, panZoomUpdate, panZoomEnd
2. New fields on PointerData to handle two-finger trackpad gesture fields (panX, panY, scale, rotation)

Design Document

Framework PR: flutter/flutter#89944

Addresses flutter/flutter#23604

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide] and the [C++, Objective-C, Java style guides].
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See [testing the engine] for instructions on
  writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the [CLA].
• All existing and new tests are passing.

[dkwingsmt]

LGTM

[goderbauer]

RSLGTM assuming no changes since the previous PR to this code