[NavigationDrawer] Allow users to scroll to dismiss on lower resoluti…

…on devices. (#8503)

This change allows `currentlyFullscreen` property on [`MDCBottomDrawerContainerViewController`](https://github.com/material-components/material-components-ios/blob/develop/components/NavigationDrawer/src/private/MDCBottomDrawerContainerViewController.m) to become `NO` on lower resolution devices. Currently this property is always `NO`. This doesn't allow the code within `- (void)scrollViewWillEndDragging:withVelocity:targetContentOffset:` to be executed.

## Testing
1. Set `preferredContentSize` on the headerVC of a Navigation Drawer example to 80.
2. Set `preferredContentSize` on the contentVC of the same Navigation Drawer example to a value less than 240. 
3. Open the example on a iPhoneSE
4. Rotate to landscape.
5. Try to swipe to dismiss the drawer.

Closes #8454

components/NavigationDrawer/src/private/MDCBottomDrawerContainerViewController.m

@@ -661,7 +661,7 @@ - (void)updateViewWithContentOffset:(CGPoint)contentOffset {
                                                        transitionRatio:transitionPercentage];
 
   [self updateDrawerState:transitionPercentage];
-  self.currentlyFullscreen = self.contentReachesFullscreen && headerTransitionToTop >= 1;
+  self.currentlyFullscreen = self.contentReachesFullscreen && contentOffset.y > 0;
   CGFloat fullscreenHeaderHeight =
       self.contentReachesFullscreen ? self.topHeaderHeight : [self contentHeaderHeight];