Add FontManager API and font manager shell commands

FontManager is an interface of communicating with FontManaserService.
With this CL, system apps can know the primitive information about
what font files are installed and how it is configured.

This CL also adds shell command of dumping font configuration.
Example usages are:

  # dump primitive font configuration.
  adb shell dumpsys font

  # dump fallback font list
  adb shell cmd font dump serif

Bug: 173619554
Test: atest FontManagerTest
Test: Manually confirmed above commands works.
Change-Id: I5cb855308e199ac38bd7b56b60821346247bdce3