Diacritics compositions / dotted circle ligatures

To be able to support diacritics compositions, google fonts need to include support for
`dotted circle + *` ligatures (type 4 in GSUB)
Afaik there's no that feature yet.

Ref https://docs.microsoft.com/en-us/typography/opentype/spec/gsub, https://docs.microsoft.com/en-us/typography/script-development/arabic

That can be done as a separate tool, but having that in google fonts would enable so many world uses, like vedabase.io etc

_Originally posted by @dy in https://github.com/google/fonts/issues/1808#issuecomment-766894187_