Automation Editor - Straighten out draw line function

[zonkmachine]

Nudge the line (biggest improvement) and quantize x arguments to AutomationEditor::drawLine(..).

Fixes #3995

[zonkmachine]

This isn't one issue only. I've fixed up AutomationEditor::drawLine(...) but there is still things to do.
In AutomationEditor::mousePressEvent(...), if the shift button is held and the left mouse button is pressed, we first draw a line and then carry on with the final point and create a drag value as the last point is selected for dragging. The magic happens here. Many times it's the last or next to last point that is off so I think this is related to a rounding off error and/or quantization in the above mentioned functions and in AutomationPattern::setDragValue(...). If you draw your points close to their quantized values there is little risk of a draw error. If you draw a line with steep angles between two points and aim for slightly to the left of the left point and to the right of the right one (picture), you will get a draw error. The closest points on both sides will snap to the same level. Setting m_drawLastTick = new_time; after it = time_map.find( new_time ); avoids this but just pushes the error around.

Edit: this specific behaviour was introduced in this PR This part reverted, issue fixed.

[zonkmachine]

I think it's out of scope for 1.2 to fix this and suggest that we merge #3997 and leave #3995 open.

[zonkmachine]

Quantize drawline() input. The line is drawn from a mix of unquantized x0, x1 input values and the quantized deltax, and will sometimes not draw correct.

[zonkmachine]

Fixed. I'll merge this tomorrow if there are no objections.