Linear and Radial Gradients on main branch

[AshishS-1123]

Summary / How this PR fixes the problem?

Following features will be implemented in this PR

• [x] Create a Pattern Component to represent different types of Fill a canvas item can have (Solid, Linear and Radial)
• [x] Create widget for choosing between different types of pattern (Widgets.PatternTypeChooser)
• [x] Create widget for adding, removing and modifying stop colors on patterns.
• [x] Render the selected Pattern on Canvas.
• [x] Create Nobs for modifying start and end points of gradients on canvas item.
• [x] Allow saving patterns to colors container
• [x] Show the created pattern on the ColorButton in fills panel.

Blending Cairo.Patterns requires a little bit of math (Linear Interpolation. Will probably implement it in another PR

Steps to Test

• Draw some canvas item (like Rectangle or Ellipse).
• Click on the ColorButton in the Fills Panel. This should open a popover.
• At the top of the popover, you should see the PatternTypeChooser. Select whichever mode you want,
• For linear and radial gradients, you can use the GradientEditor widget below PatternTypeChooser to add stop colors and change their colors.
• With the Popover open, you can also move the gradient nobs around to change position of the pattern.

After creating a pattern, click on the + button to add this pattern to the Global colors. You can then apply the same pattern to any other canvas item by clicking on it.

Screenshots

Known Issues / Things To Do

• Blending Lib.Components.Pattern has not been implemented yet.

This PR fixes/implements the following bugs/features:

• Fixes #605