Add various shortcuts that were missing from the industry compatible
key-map. Various grease pencil shortcuts that were intended to be there
are now present.
These issues are now fixed:
- `Alt A` = Missing from GP sculpt mode.
- `Shift S` = Missing.
- `Shift Alt S` = Insert Blank Keyframe - Not added to Edit mode.
- `Y` = Active Layer Menu - Not added to Edit mode.
- `Shift Y` = Merge Down - Does not exist.
- `Shift Backspace/Delete` = Delete All Active Frames is missing from
every mode except Draw.
- `Backspace/Delete` = Delete Menu is missing from all modes except
Edit.
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