Fix trackpad code completion scrolling

[adamscott]

This PR makes it so that the code stops interpreting past the fact the gestures done inside the code completion window.

This PR also sets code_completion_pan_offset to 0 as otherwise, you could do multiple gestures past the beginning of the list or the end, and it would take time to "return" to the list afterwards, as there is no upper/lower limit to the offset.

Before

before.webm

After

after.webm

Fixes #94415

[adamscott]

cc. @bruvzg

[Repiteo]

Thanks!