Improved js_modules support

[WebReflection]

This MR allows MicroPython to use polyscript.js_modules same way Pyodide supports it already by doing the following:

• removed the Proxy from the Worker as it's causing weird bugs/behaviors in MicroPython only
• resolved as either static field or lazy accessor (getter) both modules pre-fetched for the worker and those to resolve at their first access from main
• added smoke tests for both Pyodide and MicroPython and tested everything is fine
• registered both polyscript and polyscript.js_modules to resolve the magic behavior in Pyodide impossible to replicate in MicroPython

The latter point means that a similar solution can be used to fix pyscript/pyscript#1899 too so that we don't need anymore to pollute the global with another entry as js_modules is and both py and mpy can work seamlessly when it comes to import modules.