[Feature] Add icon editor block

[laurensvalk]

Is your feature request related to a problem? Please describe. There are currently no convenient ways to display icons using the block language.

Describe the solution you'd like Expose the icon display method in a block. It could have the builtin icons as a visual dropdown shadow input.

Users could override the shadow input with their own grid input, for which an editor already exists in Blockly.

Like custom colors, maybe defining icons should happen in the setup.