feat: long hold pen for lines/shape recognition

[Doublonmousse]

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This is still a draft but I want to be sure that the general structure is correct before going further. At the moment it always transform the pen path into a line between the start and end position if the gesture is detected.

For now what I'm worried about

• [ ] does the current implementation works without mutation issues on the engine ?
• [ ] I'm not fully sure the use of the OneOffTask is completly correct
• [ ] tweak the settings and test it with touch/pen input (does it work correctly).

Then there is a lot of functionality missing

• [ ] toggle the setting in the UI (and have this propagate into the rest of the code so no power is lost detecting a gesture for nothing)
• [ ] emit shapes with the correct stroke width (and extend it further than just lines, for now I'm not entirely sure how that could be done, there's probably new methods to add to the shaper to be able to do that from a single function call)
• [ ] implement the shape recognizer. For now there is no shape recognizer as I was only searching for a way to make the gesture work. At least the general form of the recognizer should be a `PenPath -> Option<Shape>' so it either recognizes something and returns it or it doesn't.

Issues : #384 and maybe #120 if the last point is developped further than just lines/not lines

[PeterWang-dev]

Any progress on this PR?