Update fontchain_lint to work with multiple emoji fonts

This change include following fix for fontlint_chaing:
- Validate font_fallback.xml instead of fonts.xml.
  The fonts.xml is deprecated and font_fallback.xml is the
  latest font config file.
- Remove PostScript name validation.
  This is now validated in the CTS. So no need to validate
  it in fontchain_lint
- Skip the coverage check if the Unicode version is ahead of
  the given font version.

Bug: 358182138
Test: lunch aosp_husky-trunk_staging-eng && m fontchain_lint
Test: lunch aosp_husky-trunk-eng && m fontchain_lint
Flag: None build config change
Change-Id: I8ab5ffb586855d6677a820af89b2d56f910c70e1