Add option to place icons in screenshots - #4677

Feature

An icon tool enabling the user to place icons to annotate their image, such as the ones seen in the screenshot below:

The icon tool's button

List of current icons available in this PR (Much more can be included)

The user can save the screenshot with these icons included.

Technical Implementation Notes

• Adds a new Icon tool to the capture toolbar
• Uses built-in symbols instead of external icons at the moment
• The placed icons can be modified similarly to other elements currently available in the application
• Keeping this first version of the feature small by using a fixed set of built-in symbols

Testing

• Built and executed Flameshot locally
• Selected Icon tool and placed icons in screenshot
• Icons appear as placed in saved image
• All existing annotation tools still work as expected

Related Issue

Closes #4656