SVG animation needs to be timed according to fvar and avar, not gvar

[Lorp]

The SVG animation exporter currently ignores the ‘fvar’ and ‘avar’ tables, so all the deltas are timed according to the -1, 0, +1 normalized scale. This results in animations with min at t=0, default at t=0.5, and max and t=1. Axes in many fonts have their default closer to min than to max, so current behaviour results in unexpected timing behaviour.