Document glyf on-curve point interpolation

[bungeman]

Description

In "Simple glyph description" there should be some documentation along the lines of "If there are two off curve points in a row then the missing on curve point is implicitly located at the midpoint between the two off curve points."

Page URL

https://learn.microsoft.com/en-us/typography/opentype/spec/glyf

Content source URL

https://github.com/MicrosoftDocs/typography/blob/live/typographydocs/opentype/spec/glyf.md

[Lorp]

The text would need to be careful to avoid implying that the implicit point receives its own point ID in hinting and component attachment.