Introduce set/getFontVariationSettings.

This is 2nd attempt of I249d464f8cdaa56017a987588b94ed685aadeb58.
The original CL was reverted due to conflicting with another CL submitted
before.
Nothing has changed except for following class name changes.

Here is the original commit message of reverted change.

This CL enables developers to specify axis values to the underlying
font collection. The specification of the font variation settings is
the same as the CSS font-variation-settings attribute in CSS working
draft as of 2016-11-30.

Code example: Here is an example to set width 100 and weight 1.5.

  TextView tv = (TextView) findViewById(R.id.textView);
  tv.setFontVariationSettings("'wdth' 100, 'wght' 1.5");

Bug: 33062398
Test: Manually done. Ran FrameworksGraphicsTests, CtsGraphicsTestCases
      and CtsWidgetTestCases

Change-Id: I9cdfbdecc87c995d805096883ef2652768c6c21e