Add proper angle widgets (4.3)

This MR adds new angle widgets to choose angles:

The changes basically do the following:

• add an angle gauge widget (a circular widget that allows to choose an angle) that:
  • can be changed with the keyboard (up/down/left/right keys), with the mouse wheel or the mouse (clicking and dragging around)
  • has snapping to multiples of a custom angle by using ctrl + up/down/left/right keys, ctrl + mouse wheel or by click and dragging close to the gauge
  • has a custom reseting angle that can be set by double clicking
• add a generic angle selector widget that puts together the angle gauge to quickly choose an angle, a spin box to fine tune the value of the angle, and some options to flip the selected angle
• put the angle selector in relevant places. The idea is to put it everywhere it is suitable

NOTE: I'll make a list of the relevant widgets where the angle selector could be put before making any changes, in case some of them need discussion. I'll make a commit for each of them. If anyone has suggestions for places where to put it, write here.

Places where to put the angle selector:

• Filters
  • Blur
    • Blur (image)
    • Lens Blur (image)
    • Motion Blur (image)
  • Map
    • Phong Bumpmap (image)
• Generators
  • Gradient (image)
  • Pattern (image)
  • Screentone (image)
• Dockers
  • Overview (image)
  • Artistic Color Selector (image)
• Tool Options
  • Edit Shape Tool (Ellipses) (image)
  • Calligraphy (image)
  • Shape Tools (image)
    • Rectangle Tool
    • Ellipse Tool
    • Polygon Tool
    • Polyline Tool
    • Bezier Curve Tool (image)
    • Freehand Path Tool
  • Dynamic Brush Tool (image)
  • Multibrush Tool (image)
  • Fill Tool (image)
  • Bezier Curve Selection Tool (image)
• Other
  • Status Bar (image)
  • Image->Rotate->Rotate Image... (image)
    • Layer->Transform->Rotate->Rotate Layer...
    • Layer->Transform All Layers->Rotate->Rotate All Layers...
  • Image->Shear Image... (image)
    • Layer->Transform->Shear Layer...
    • Layer->Transform All Layers->Shear All Layers...
  • Layer->Split->Clones Array... (image)
  • Layer->Layer Style... (image)
• Brush Settings
  • Pixel Engine
    • General->Brush Tip->Auto->Angle (image)
    • General->Brush Tip->Predefined->Rotation (image)
    • Masked Brush->Brush Tip->Auto->Angle (image, same as general->brush tip)
    • Masked Brush->Brush Tip->Predefined->Rotation (image, same as general->brush tip)
  • Color Smudge Engine
    • General->Brush Tip->Auto->Angle (image, same as pixel engine)
    • General->Brush Tip->Predefined->Rotation (image, same as pixel engine)
  • Sketch Engine
    • General->Brush Tip->Auto->Angle (image, same as pixel engine)
    • General->Brush Tip->Predefined->Rotation (image, same as pixel engine)
  • Bristle Engine
    • General->Brush Tip->Auto->Angle (image, same as pixel engine)
    • General->Brush Tip->Predefined->Rotation (image, same as pixel engine)
  • Spray Engine
    • General->Spray Area->Angle (image)
    • General->Brush Tip->Auto->Angle (image, same as pixel engine)
    • General->Brush Tip->Predefined->Rotation (image, same as pixel engine)
    • General->Shape Dynamics->Fixed Rotation (image)
  • Hatching Engine
    • General->Brush Tip->Auto->Angle (image, same as pixel engine)
    • General->Brush Tip->Predefined->Rotation (image, same as pixel engine)
    • General->Hatching Options->Angle (image)
  • Clone Engine
    • General->Brush Tip->Auto->Angle (image, same as pixel engine)
    • General->Brush Tip->Predefined->Rotation (image, same as pixel engine)
  • Tangent Normal Engine
    • General->Brush Tip->Auto->Angle (image, same as pixel engine)
    • General->Brush Tip->Predefined->Rotation (image, same as pixel engine)
  • Deform Engine
    • General->Brush Size->Angle (image)
  • Filter Engine
    • General->Brush Tip->Auto->Angle (image, same as pixel engine)
    • General->Brush Tip->Predefined->Rotation (image, same as pixel engine)

Formalities Checklist

• I confirmed this builds.
• I confirmed Krita ran and the relevant functions work.
• I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
• I made sure my commits build individually and have good descriptions as per KDE guidelines.
• I made sure my code conforms to the standards set in the HACKING file.
• I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.