Use floating-point value for Drawable level

This allows us to run fine-grained level animations.

Backwards compatibility:
Another CL will add DrawableCompat.setLevel(float) to forward calls to
the existing integer-based method. For callbacks, developers can override
onLevelChanged(int) and use DrawableCompat.getLevelFloat() to obtain the
floating-point level. Overriding onLevelChanged(float) will only work on
current API.

Bug: 23566299
Change-Id: I431fe6f3679c8f23f9cf3c2bb1f92a4059ee68e3

graphics/java/android/graphics/drawable/DrawableContainer.java

@@ -322,7 +322,7 @@ public class DrawableContainer extends Drawable implements Drawable.Callback {
     }
 
     @Override
-    protected boolean onLevelChange(int level) {
+    protected boolean onLevelChange(float level) {
         if (mLastDrawable != null) {
             return mLastDrawable.setLevel(level);
         }
@@ -510,7 +510,7 @@ public class DrawableContainer extends Drawable implements Drawable.Callback {
         d.setVisible(isVisible(), true);
         d.setDither(mDrawableContainerState.mDither);
         d.setState(getState());
-        d.setLevel(getLevel());
+        d.setLevel(getLevelFloat());
         d.setBounds(getBounds());
         d.setLayoutDirection(getLayoutDirection());
         d.setAutoMirrored(mDrawableContainerState.mAutoMirrored);