Switch timeline clip context menu to QWidget instead of Qml.

Fixes the "cannot edit text" issue on Windows and makes keyboard shortcuts appear again in menu
1 job for master in 16 minutes and 4 seconds (queued for 1 minute and 40 seconds)
Status Job ID Name Coverage
  Build
passed #29783
linux kf5-qt5 qt5.12

00:16:04

20.0%