Refactor block definitions patched in scratch-gui/src/lib/blocks.js

[gonfunko]

The scratch-gui package patches/overrides a number of block definitions in src/lib/blocks.js, generally when they need dynamic state depending on the state of the VM. We should likely do one of the following:

• Remove the body of the block definitions in scratch-blocks, since they're being overwritten
• Move the dynamic bits out of scratch-gui and into scratch-blocks
• Perhaps something else?

[cwillisf]

I'd lean toward "Move the dynamic bits out of scratch-gui and into scratch-blocks" as long as the implementation effort is reasonable