Update Blockly code demo to pull in colour blocks from plugins

[rachel-fenichel]

Check for duplicates

• I have searched for similar issues before opening a new one.

Problem

Necessary cleanup after deleting fields from core. The code demo has fields and blocks that have been deleted, and we know that the code demo gets used for storing full programs.

Request

The fix is to pull in and install the colour blocks from the new plugins. This has to happen after the blockly-samples blocks_for_fields branch is merged and the plugins are published.

Alternatives considered

Delete the blocks from the demo. We shouldn't do this unless we can verify (through inspecting saved code) that they are never used. That verification is probably more work than just importing the blocks.

Additional context

No response

[rachel-fenichel]

Depends on fixing RaspberryPiFoundation/blockly-samples#2243 and doing a release of plugins.

[rachel-fenichel]

@NeilFraser this issue tracks adding the colour blocks to the code demo, if you conclude that they are in use in saved code. If you make it obsolete by deleting the blocks, please also close this.