Add a function to scroll to top when the header view is sticked.

[wanderingfairy]

To fix the issue in #67, a function was added.

The reason why changes to scrollView.contentOffset are ignored when the headerView is in the sticked state is related to the scrollView.observe() method.

As soon as scrollView.contentOffset is changed, the parentScrollViewDidScroll(_:) is called immediately, and parentContentOffsetY is compared with headerStickyHeight.

And because parentScrollView.contentOffset.y is reset based on the comparison result in the switch statement, the 'scroll to top' operation desired by the user is not executed.

In order to bypass parentScrollViewDidScroll(_:) with minimal impact on other parts, I added a function that disables parentKeyValueObservation for 2 seconds. If the deactivation time is too short, contentOffset.y is intercepted by the observe() method before moving to the top, so I set it to 2 seconds.

contentOffset.y is reset to zero for 2 seconds when parentKeyValueObservation is disabled.

Like resetCurrentChildViewControllerContentOffsetY or resetOtherCachedChildViewControllerContentOffsetY, the parentViewController needs a method to scroll to the top.

If you call self.resetCurrentParentViewControllerContentOffsetY(scrollView) in SegementSlideViewController, the scrollView is scrolled to the top of the scrollView even if headerView is sticked.

Thank you.

[codecov]

Codecov Report

Merging #86 (c3fb911) into master (34665bd) will decrease coverage by 0.94%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #86      +/-   ##
==========================================
- Coverage   73.58%   72.64%   -0.95%     
==========================================
  Files          11       11              
  Lines         106      106              
==========================================
- Hits           78       77       -1     
- Misses         28       29       +1     

Impacted Files	Coverage Δ
Source/Switcher/BadgeView.swift	92.53% <0.00%> (-1.50%)	⬇️