Removes the once_cell dependency, instead using std::sync::OnceLock and a
minimal polyfill for std::sync::LazyLock, which may be stabilized soon
(see rust-lang/rust#121377).
This should not require a bump in MSRV, as OnceLock was stabilized in 1.70,
which this crate is using.
Replace the `CustomCursorBuilder` with the `CustomCursorSource` and
perform the loading of the cursor via the
`EventLoop::create_custom_cursor` instead of passing it to the builder
itself.
This follows the `EventLoop::create_window` API.
Creating window when event loop is not running generally doesn't work,
since a bunch of events and sync OS requests can't be processed. This
is also an issue on e.g. Android, since window can't be created outside
event loop easily.
Thus deprecate the window creation when event loop is not running,
as well as other resource creation to running event loop.
Given that all the examples use the bad pattern of creating the window
when event loop is not running and also most example existence is
questionable, since they show single thing and the majority of their
code is window/event loop initialization, they wore merged into
a single example 'window.rs' example that showcases very simple
application using winit.
Fixes#3399.
* Refactor winit-specific cursor logic out of appkit module
* Add relevant AppKit features that we depend on
* Use icrate's NSImageRep and NSBitmapImageRep
* Use icrate's NSImage
* Use icrate's NSCursor
* Use icrate's NSAppearance
* Use icrate's NSScreen
* Use icrate's NSButton
* Use icrate's NSAppKitVersionNumber
* Use icrate's NSTextInputContext
* Use icrate's NSColor
* Use icrate's NSEvent
* Use icrate's NSMenu and NSMenuItem
* Use icrate's NSPasteboard
* Use icrate's NSResponder
* Use icrate's NSTextInputClient
* Use icrate's NSView
