PencilBrush SHIFT/straight line functionality

[ShaMan123]

This PR adds the ability to draw a straight line when pressing the shift key or when setting drawStraightLine to true.

// Override `shift` functionality
brush._detach();

// Restore `shift` functionality
brush._attachKeyboardListeners();

// direct setter
brush.drawStraightLine = true;

Logic

When drawStraightLine = true the brush simply pops the last point and adds the new one

Live Example

[ShaMan123]

Needs to be validated against #6966

[ShaMan123]

It is why there's a merge conflict

[asturur]

so master is at < l -1 to fix a tail issue with decimate.
Why did you add the equal in?
If you explain we can solve the conflict.
But to me is not clear why this has changed.

[ShaMan123]

The logic of straight line pops the last point and push the last pointer.
When mouse up fires and drawStraightLine=true it decimated the end and removes the last straight line part.
I don't know/understand what decimate does so I don't want to propose anything but this can be mitigated by pushing another point on mouse up if drawStraightLine=true (I don't like it though)

[ShaMan123]

You can see/test
https://codesandbox.io/s/blue-shape-evc6t?file=/src/ShiftBrush.js:9550-9576

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[ShaMan123]

this should be merged

[ShaMan123]

@asturur please re open and merge

[asturur]

Sorry this PR was good after my conflict resolve, eventually waiting for tests to pass i forgot about it.