No, I wouldn't call it an appoggiatura. But that distinction has nothing to do with duration.
It depends on which textbook you use. It depends on the assumptions of said textbook. It depends on when the textbook was written.
The historical use of the term appoggiatura is about a "leaning" note that falls on a strong beat and resolves to a weak one. (...
Yes, this is an appoggiatura.
One of the things to remember with non-chord tones is that duration isn't really important; even if the non-chord tone takes up 99% of the measure and the chord tone only takes up 1%, that doesn't switch which tone is a part of the chord. It's all about the underlying harmony. (The meter, however, can be important, and some ...
The first example is obviously a multi-note appoggiatura with the same properties of your simple example:
Start on the beat of the main note
shorten that accordingly to fit the ornament in.
You are probably right on the second example, the ornament is played after the trill but the following notes and possible ornaments may influence this.
The notation with an appoggiatura, which the text calls a turn figure
That satisfies the simple definition of a turn as "a short figure consisting of the note above the one indicated, the note itself, the note below the one indicated, and the note itself again."
However, a turn notated as
is perhaps more generally played as an ornament on the ...