Redesign the fallback XML syntax to be able to have static and variable font.

Defining all instances of weight instance causes memory bloat. To reduce
the memory usage, use dynamic font instance.

Bug: 280011317
Test: atest UpdatableFontDirTest UpdatableSystemFontTest
Test: atest GtsFontHostTestCases FontManagerTest CtsTextTestCases
Test: atest CtsGraphicsTestCases PersistentSystemFontConfigTest
Change-Id: Idd7b8cf8984e44b5864124277a01586e14894be0