Introduce early exit path for non resource path.

Developer can specify android:fontFamily with three ways, pre-defined
font family name, e.g. "sans-serif", path to the font file in resource
directory, e.g. "res/fonts/Roboto-Regular.ttf", or path to the XML font
family file, e.g. "res/fonts/Roboto.xml".

Resources.getFont treats font files and XML files but pre-defined family
name is handled by TextView. Thus, we can early exit if the passed value
is not likely resource path.

This improves the inflation performance.
The score without this patch:
gfx-avg-frame-time-50: 6.9
gfx-avg-frame-time-90: 9.4
gfx-avg-frame-time-95: 10.4
gfx-avg-frame-time-99: 16.7

The score with this patch:
gfx-avg-frame-time-50: 7.0
gfx-avg-frame-time-90: 8.9
gfx-avg-frame-time-95: 9.7
gfx-avg-frame-time-99: 16.5

Measured on bullhead-userdebug.

The APCT perf test improves from
String FontFamily: 200,086 -> 132,561
File FontFamily  : 199,256 -> 161,843
XML FontFamily   : 203,681 -> 158,553

Measured on angler-userdebug.

Bug: 38232467
Test: UiBenchmark
Change-Id: Ia601ae7207ae8c60848c9efdbb9396267a57257c