feat: compiled elements

[HigherOrderLogic]

Closes #6.

Allow user to use slint::include_modules!() and include compiled elements at compile-time.

It works (take a look at the example), but there are still some caveats/aspects I still dont like:

• there is currently no way for users to open a popup if they use compiled elements
• title-based lookup required lots of heuristic mappings, and the implementation still relies on order-based lookup (using ordermap) for namespace for protocols-restricted reason
• the Platform trait implementation is kinda long, and I feel the existing code can be reused better to shorten it
• slint-intepreter is still not optional, may make it later
• I cant test multiple monitors since I dont have the hardware

Also, at my liberty, I have added some nice QoL improvements such as auto width/heigh based on anchors if unspecified.

[drendog]

thanks, I'll take a look at it tomorrow