Wire up more properties in handlers and support flex.

A problem with extrapolation means that the interpolation tests in this CL don't test the property handler lists, as they are expected to fail.

I've bypassed the extrapolation bug locally in order to check this CL. The testing will work when the extrapolation bug is fixed.
> shorthands should list the dashed names too

Doing this means that we end up with dashed member identifiers in our normalized keyframes.