Add check: GF central repo static files should not have extras, should be a 'full house'

[davelab6]

Observed behaviour

In google/fonts#2644 (comment) I noted there were some 'extra' files in the static directory, that were not corresponding to the files listed in the METADATA file for the family.

Expected behaviour

I propose to add check a GF profile check on the "downstream" GF central repo folders: They should not have extra files, and when a VF is used, if there are statics, they should exist for every 100 stop along the Weight axis. Eg, a Weight axis of 400 to 700 should have statics for 400, 500, 600 and 700 if any statics exist.

[felipesanches]

thanks, @davelab6