Support pinch to zoom gesture for both touch and pointer events

[samelhusseini]

The basics

• I branched from develop
• My pull request is against develop
• My code follows the style guide

The details

Resolves

#1295

Proposed Changes

Two major proposed changes:

• Support for pointer events (Supported on latest Chrome and Edge)
• Support for multi-touch, zooming on pinch.

Reason for Changes

Pinch to zoom is more natural on touch devices!

Test Coverage

Tested manually on various touch devices, including:

• Pinch to zoom using two fingers
• Drag a block and then place another finger (should continue to drag)
• Drag the workspace and then place another finger (should continue to drag)

Tested on:

• Desktop Chrome
• Desktop Firefox
• Desktop Safari
• Windows Internet Explorer 11
• Windows Edge
• Surface Book (touch)
• IE, Chrome, Firefox and Edge
• IOS 11
  • Safari and Chrome
  • iPhone & iPad
• Android 8
• One Plus 5.
• Chrome and Firefox

Additional Information

The PR doesn't enable touch gestures by default.

Other things not in this PR, but to consider for future PRs:

• pinches can only start within the first n ms after the touch starts.
• a workspace drag can be "upgraded" into a pinch if done within a certain distance of another pointer and within a certain timeframe. In the hope of making it feel more "natural".

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[samelhusseini]

I signed it!

[googlebot]

CLAs look good, thanks!