Merge remote-tracking branch 'goog/ub-calculator-calculus'

* goog/ub-calculator-calculus:
  Fix tap handling in CalculatorPadViewPager
  Don't use Fragment#getContext()
  Polish layout configurations
  Further iterate over ViewGroups to en/disable children.
  Display error message onEquals with invalid expression
  Draw the toolbar on top
  Add digit separators to pre-evaluated results
  Fix formula TalkBack
  Fix TalkBack for advanced panel
  Crush pngs -> save space
  Add digit grouping to display
  Ensure formula/result textSize is correct
  Scale error messages and prevent wrapping
  Make Calculator compatible with API 21+
  Adjust padding for some layouts.
  Drop height bucket from 569dp to 500dp.
  Show result in ERROR mode for one line displays.
  Calculator multiwindow support R3.
  Make arccos call the correct function
  Calculator multiwindow support.
  Ignore "=" if formula contains no operators
  Handle font with missing FIGURE SPACE.
  Ensure CalculatorText is at least as wide as it's container
  Show toolbar when DEG/RAD mode matters
  Remove CAB workaround for N+ devices
  Stop the action mode in Activity#onBackPressed()
  Don't intercept "BACK" key events
  Fix hw keyboard support
  Fix result positioning on evaluate
  Refactor arithmetic code.  More symbolic result tracking.
  Wrap CalculatorText in custom HorizontalScrollView.
  Add contentDescription for empty formula view.
  Correctly handle parenthesized percent expressions
  Copy and truncate rational results exactly

Change-Id: I175f23a52ac17ec3e62594df8ba584e8926ca6dd