[3.15] gh-150831: docs: clarify generator, generator function, and generator iterator...

[3.15] gh-150831: docs: clarify generator, generator function, and generator iterator in glossary (GH-150905) (#151840)

gh-150831: docs: clarify generator, generator function, and generator iterator in glossary (GH-150905)
(cherry picked from commit 1de86e1492af92f4b18aad94390bcd4336e579ab)

Co-authored-by: Aniket <148300120+Aniketsy@users.noreply.github.com>