Always calculate textSize in CalculatorText#onMeasure

Bug: 26934901

- Don't gate the minimum height and variable text size calculations
  based on the width constraint. That constraint may remain constant
  even though other configuration parameters are changing. It's
  sufficient to just not invoke the text size change listener in
  onMeasure to prevent unnecessary animations.
- Also suppressed unchecked cast warning in CalculatorExpr.

Change-Id: Ia402cdabdf7b0864fcbb3017ab85bb4038409da8