Improvements to tidy_override(): make extend = TRUE by default, allow data frame argument to `glance`

[hughjonesd]

extend = FALSE by default is just a PITA and constantly leads to surprises. Also, let glance take a data frame - a common pattern is using glance on the original model, then running e.g. coeftest and tidy_overriding that.

[hughjonesd]

Data frame argument to glance should now work (and maybe did before, sometimes). extend = FALSE is a breaking change so will have to wait a little; I've improved the error messages.