Allow fadingEdgeLength to be set independently on the start and end of the scrollview

[markv]

Summary:
Allows the start and end of the scrollview to be faded to different values independently by passing an object containing a "start" and "end" value to the fadingEdgeLength prop.

To support non-uniform edge lengths we use the FadingEdgeStrength api to set different values for the start/end of the scrollview. The FadingEdgeStrength value is multiplied by the FadingEdgeLength value internally by Android when drawing the view.

Because the value of FadingEdgeStrength is required to be between 0 and 1, we set setFadingEdgeLength to the max value and set the smaller side as a percentage of that value.

Changelog: [Android][Added] Allow fadingEdgeLength to be set independently on the start and end of the scrollview

Reviewed By: martinbooth

Differential Revision: D74222606

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D74222606

[react-native-bot]

This pull request was successfully merged by Mark Verlingieri in a21a4b8

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[facebook-github-bot]

This pull request has been merged in a21a4b8.

[pkfms]

a21a4b8#commitcomment-164494231

Looks like this did go into RN 0.81 - however, for some reason now the beginning of the content already fades at vertical scroll position 0 - which means the content is already fading on start although nobody scrolled so far. This is independent whether you use a number now or { start, end } construct. Both is not the case in RN 0.80.2 - here only in case you scroll from start to a position > 0 the start is fading. Is this the intended behavior (as from my point of view this is a breaking change). Besides, in general I think it's a good idea to control start and end - but this way we no longer can use fadingEdgeLength at all ...