Review API Documentation of new platform/backend API

[tronical]

This is a reminder task to go through the documentation of the new window and backend traits, the new functions added to the api::Window.

[ogoffart]

This include:

• the whole platform module.
• Window::dispatch_event and the WindowEvent structure
• the setter and getter for the size and position in the Window struct. As well as the Physical and Logical size and position type and the scale factor
• Window::has_active_animations
• the format macro
• some new feature flags
• MCU documentation

[ogoffart]

We'll make an API review meeting tomorrow (Tuesday 06.10) at 10:00 CEST (Berlin time) on our Mattermost (everyone welcome)

[tronical]

Notes from the meeting:

Version number

We decided to increase the version to 0.3.0.

platform module

• [x] swrenderer -> slint::platform::software_renderer (T)
• [x] Always compile the software renderer, independent of the renderer-software feature on the API crate (O)
• Not possible: Try to see if set_platform can be changed to take Into<Box<...>> (S)
• [x] Introduce SetPlatformError enum that has AlreadySet (S)
• [x] return an error from the function of the EventLoopProxy (O)

SoftwareRenderer (O)

• [x] remove the =0 for BUFFER_COUNT
• [x] rename BUFFER_COUNT to MAX_BUFFER_AGE
• [x] Hide implementation of Renderer trait from the documentation (don't show internal text_size etc. functions)

TargetPixel trait (O)

• [x] Rename to_fill to slice in blend_slice (24244e3c7cfedfa8590942774466c2a6f69a8dff)

slint crate features (O)

=> https://github.com/slint-ui/slint/issues/1609

• [x] Remove renderer-software feature, always support it in the winit backend.
• [x] Make sure the error message if no "gl" renderer is enabled is sensible
• [x] Move log feature out of the "Backends" section (#1600)
• [x] Remove compatibility features (also from cmake and interpreter, etc. crates)
• [x] Rename eventloop- to backend-
• [x] Remove the renderer-qt as an alias
• [ ] renderer-* not strongly depend on winit in the selector
• [ ] Documentation should include a matrix/table of supported combinations

slint::testing module (O)

• [x] Move to the i-slint-backend-testing crate (#1596)

slint::api::Window

• [x] Try to get rid of WindowHandleAccess trait (alternative: free standing function to get window inner), otherwise try to hide the docs for impl WindowHandleAccess (S)
• [x] Fix docs for scale_factor to not mention euclid (S)
• [x] Replace set_position/position/set_size/size with (S)
  • rust: set_physical_position/set_logical_position/physical_position/set_physical_size/set_logical_size/physical_size
  • js: physical_position and logical_position properties

[tronical]

This is done. There's a pending discussion about the type names WindowSize vs. RequestedSize vs. RequestedWindowSize but that's orthogonal and we might just skip it :)