Implement `iced_piet` renderer

[hecrj]

iced currently has 2 renderers: iced_wgpu and iced_glow. Both of them are built directly on top of relatively low-level graphics APIs (WebGPU and OpenGL, respectively).

It'd be great to build additional renderers on top of higher level abstractions. Doing this should help us get a better understanding of the current limitations of the library and maybe draw some inspiration to improve our graphics APIs (specially text!).

I believe we should start with a piet renderer. piet is a nice 2D graphics abstraction maintained by the folks from druid. I think relying on piet is a great opportunity to create a bridge of collaboration between the iced and druid ecosystem in the long run!

In order to achieve this, I see a couple of new subcrates:

• iced_druid implements a new windowing shell and event loop on top of druid_shell.
• iced_piet implements the new renderer on top of piet.

[Sherlock-Holo]

@hecrj hello, is there a developing repo allow us to try the iced_druid and iced_piet?