Fixed faulty pinch gesture handler on Android when in a ScrollView/FlatList

[timbrandin]

Description

FYI this is the updated version of a previous PR for v1.6.

I noticed that ScaleGestureDetector returned zero and different values for scale and focal point as the iOS equivalent, so I suggest this solution which uses the bounding box of the touches to calculate the scale from the difference between the hypothenuse from initial touch. Similar to how PanGestureHandler calculates translation using start difference.

Also with this we get focal point in the local coordinate system of the handler view, calculated using average position of all touches. Which is what you would expect from iOS.

Before fix: https://user-images.githubusercontent.com/1715834/211769742-15890fb3-4338-435d-86a3-5e997cd47cdb.mp4

After fix: https://user-images.githubusercontent.com/1715834/211769926-9b462322-29ca-460d-b071-3ab0b4a48577.mp4

Test plan

This code has also been in production since 2021, have tested for our use case on most common android devices and versions.