Support for Blockly Themes selection

[ralphwetzel]

Initially Bart tried to import the Blockly Theme modules the conventional way:

node.themeModule = await import("/blockly-contrib/npm/@blockly___SEPARATOR___theme-" + theme + "/dist/index.js");

This yet runs into Cannot read properties of undefined (reading 'Blockly'). Looks like there's an issue with the webpackUniversalModuleDefinition implementation. I found no way to compensate for this. Bad. As [...]/src/index.js is the pure code file (not being wrapped into the webpackUniversalModuleDefinition stuff), I tried to import from there. Fails as well, as import Blockly from 'blockly/core' cannot be resolved. The good thing: We don't need this import at all! Blockly is guaranteed to be already defined! Fortunately, the Blockly Theme plugins follow a very simple & identical pattern - supporting the following hack:

• Get the script as text from the runtime.
• Remove import Blockly from 'blockly/core'; from the script.
• Replace export default ... statement by a simple return.
• Wrap this script into a self executing function, to assign its value to the Blockly.Themes object.
• Do those steps for all defined themes.
• Create a script tag and let it execute the generated code.

Works like a charm!

Closes #106

[bartbutenaers]

@ralphwetzel,

This is VERY kind of you!! Thanks a lot for this. Your way to load this is very creative. I wouldn't have thought about that myself...

@cymplecy: I had installed the blockly-themes branch from Ralph's fork, and then e.g. the Black theme looks like this:

So I have merged his changes in our master branch.