Add fonts to VariantGrid params and default Variant params
For fonts to be loaded from the templates for single-file test grids,
they must be visible from the grid as a whole, and they must be
aggregated for cases with different fonts declared in different
variants.
This change adds the fonts param to grids using _param_set, creates
it as an empty list when initializing a default variant.
In a follow-up CL in the stack, a test is created that requires the
loading of fonts and uses single-file variant grids.
Bug: 341213359
Change-Id: Id6d83d26ab4cfa9a98747d573926fc40a24ab565
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5635554
Reviewed-by: Jean-Philippe Gravel jpgravel@chromium.org
Commit-Queue: Andres Ricardo Perez andresrperez@chromium.org
Cr-Commit-Position: refs/heads/main@{#1322188}