fix(Slider): Fix issues with scrub and allowTouchTrack - #3203

What kind of change does this PR introduce?
Fixes #3087 and #3130

Did you add tests for your changes?
Yes, existing test cases were fixed, snapshots updated, and new test cases added.

Summary
This PR is a significant refactor of the Slider component. The primary driver of this change is to fix the onValueChange, onSlidingStart, and onSlidingComplete callback props, as they weren't sending in the current position. I believe they were broken when the Slider component was ported to a function component.

Before starting this update, I also realized the test scripts were failing on the Slider component. So, this PR also fixes the tests, updates the snapshots, and adds a couple new test. Unfortunately, the test coverage is lower than I'd like, but the primary reason is the Pan Gesture handlers, as they're commonly cumbersome and tedious to test with Jest.

Additionally, major kudos to @menssen for proving a great outline of what needed to be done, and providing a patch. As @menssen pointed out in his comments, his changes had been de-typescripted, so I use his changes as a starting point, added-in typescript where appropriate, and fixed/optimized other items as I came across them..

Here are some notes about the changes (again, thanks to @menssen for a fantastic starting point):

• Added useCallback() to functions within the component, and added the appropriate dependencies array. Note this change required reordering of many of these functions to eliminate compiler complaints. Unfortunately, this makes the diff a little harder to follow.
• Moved function getBoundedValue(), handlePanResponderRequestEnd(), and handleMoveShouldSetPanResponder() out of the component, as they're not dependent on any component state variables.
• Added SizableVars enum to describe possible vars managed within handleMeasure()
• Extracted setting allMeasured into a stand-alone useEffect() so it gets automatically updated whenever any of the SizableVars structures change.
• Destructured all props used within the FC so they're not passed-down unnecessarily (otherwise they get passed into the container View).
• Removed didMountRef as it really wasn't needed.
• Remove numerous cases where an optional prop was used as someProp || defaultValue, as that's not needed because in those cases the defaultProps ensure default values exist at initial render.
• Always range-bound props.value at the top of the function. This eliminated the need to bound it later (as was done multiple times).
• Changed isVertical from ref to calculated value, as it will now update if props are changed.
• Review @menssen comments re his changes; those are mostly included in this PR.

I think that captures the gist of the changes. I realize this is a large PR, so thanks in advance for review. IMO, this is a pretty important PR, as the existing implementation doesn't work in the 3.x stream. In my app, I had to remain on the 2.3 stream until. I fixed these issues.

Please let me know if there are any questions or issues.