Add family-list tag element to fonts_customization.xml

family-list can be used as a named font family definition.
Multiple families can be used as a fallback for the named
family.

Bug: 249787583
Test: atest TypefaceSystemFallbackTest FontListParserTest
Test: atest UpdatableFontDirTest UpdatableSystemFontTest
Test: atest GtsFontHostTestCases FontManagerTest
Change-Id: Ic459a533ac4b5081660c0a4a7519ef7e87a6b628