Introducing script type="dummy"

[WebReflection]

As explained in here to @ntoll pyscript/pyscript#2128 (comment)

it'd be great to have a dummy zero-runtime interpreter that we could use to:

• test interpreters capabilities
• bootstrap convoluted logic that require an interpreter without penalizing performance and without bothering the network at all
• use to just demo polyscript (or PyScript) abilities directly via JS

This MR brings the dummy module in a way that:

• it's minimalistic in size and implementation
• it brings without needing to trash stuff on the global context a module system (require(name) borrowed from CommonJS)
• it's tested and it works great ... we can use it in the current PyScript MR too to avoid bootstrapping MicroPython instead so it'd be instantaneous

@ntoll happy to approve?

[WebReflection]

before anyone asks ... using js is not a great idea because we have QuickJS and we could have any other real WASM sandbox that could use the name js so I don't feel too comfortable in using such name for the interpreter as there's nothing happening if not just code evaluation but we could have that name reserved for the future to do greater / better things.