Test blocks in Playground

[AnmAtAnm]

Problem statement

There are several block configurations that never get regularly tested because they are not present in the standard blocks. Examples:

• Empty block with a mutator (RTL Render error on block with icon and no fields/inputs #1608).
• Very long list drop down.
• Drop down with images.
• Date field blocks.
• Angle field blocks.

Proposed Solution

Add a new option "Test Blocks" to the playground toolbox-type selection. Selecting it will restart the workspace with categories of various block configurations that need testing. This keeps these block accessible testing, without modifying the standard block categories.

These blocks and their toolbox should be stored in a manner editable by the new devtools.