[BottomSheetBehavior] Allow avoiding STATE_HALF_EXPANDED

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**Is your feature request related to a problem? Please describe.**
By popular request - https://stackoverflow.com/questions/59487982/android-how-to-disable-state-half-expanded-state-of-a-bottom-sheet:
- have `behavior_fitToContents = false` to try getting the view to have 2 possible states: expanded and collapsed with app defined fixed dimensions.
- a third - `STATE_HALF_EXPANDED` state and view height is introduced that's of no use.

**Describe the solution you'd like**
A `behavior_skipHalfExpanded` property/method that would have the behavior never set `STATE_HALF_EXPANDED`.

We also happily accept [pull requests](https://github.com/material-components/material-components-android/pulls).

Start by locating BottomSheetBehavior and its existing fit-to-contents and half-expanded state handling, then inspect related tests. Define the skip behavior so fitToContents=false supports only expanded and collapsed states, and verify state transitions and the public property or method in the test suite.

Written by the indexing model from the issue text.