[Spritelab] Add Mini Toolbox to event blocks, behind experiment

[ajpal]

Experiment flag: miniToolbox

Done:

• miniToolboxBlocks as a new option in the block config
• generated code changes to make everything work
• subject/object pointer blocks

To Do:

• set up shadowing for subject and object blocks
• make the blocks within the mini toolbox shadow the costume
• add the word "sprite" on the block when there's no costume to show
• Make it configurable on levelbuilder whether or not to show the minitoolbox

Without experiment:

[jmkulwik]

NIT: Mind leaving a quick comment explaining what's going on here? It makes sense next to the visual, but is less obvious when reading the code directly.

[jmkulwik]

For PR documentation: When I first read this, I was expecting to see three different IDs (i.e. extraArgs.sprite is here twice). Why is the .sprite ID reused?

[ajpal]

When we detect an event, we call back into the interpreted code, passing in any relevant info in the extraArgs parameter. For click events, there's just one sprite, so the shape of that object is {sprite: <some id>}. For touch events, there are two sprites, so we have {sprite: <some id>, target: <some id>}
The generated code for the clicked/subject/object pointer blocks just need to evaluate to the appropriate sprite, referenced by its id, so the generated code should be {id: <some id>}. In the case of click events, the relevant id is passed in as extraArgs.sprite and in the case of touch events, the ids are extraArgs.sprite and extraArgs.target

[jmkulwik]

Super exciting that this is happening! I had one quick documentation ask, if you don't mind (and a nit). Besides that, good to go :)