This PR implements the Copy and Paste operators for GPv3. The operators are available in Edit Mode. The Copy operator copies the selected strokes/ points to a clipboard. The Paste operator pastes the strokes/points from the clipboard to the active layer. Keyboard shortcuts: - `Ctrl`-`C` for copy - `Ctrl`-`V` for paste - `Ctrl`-`Shift`-`V` for paste in the back (behind all existing strokes) Pull Request: https://projects.blender.org/blender/blender/pulls/114145