This PR adds a tool to compare page transitions between Flutter and native iOS.
Best effects are achieved when testing on a real device with a ProMotion display (simulators and non ProMotion devices also work but expect loss of precision on the graph due to twice as long frame times).

Features:

• Resizable transition graph created in real time
• Changeable resolution of the graph
• Option to globally slow down the animations by 5 times
• One button to trigger transition on both platforms

Things to consider:

• Trigger transitions at the same vsync signal
• Pass touch events to allow for analyzing animations of pages dropped mid-swipe
• Find out if there is a better way to measure transition progress in Flutter

Fixes flutter/flutter#22862

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 the [Flutter Style Guide] recently, and have followed its advice.
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• All existing and new tests are passing.