eframe: Use objc2 and its framework crates (#4395)

These are a replacement to the `objc` and `cocoa` crates.

This PR prevents:
- An extra copy when creating `NSData`
- A memory leak when creating `NSImage`
- A memory leak when creating `NSString`

And is generally a readability improvement.

Note that we define `NSApp` manually for now, the implementation in
`objc2-app-kit` is currently suboptimal and wouldn't allow you to check
whether the NSApplication has been created or not.

Related: https://github.com/emilk/egui/issues/4219, this should nicely
coincide with the Winit `0.30` release.

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

deny.toml

@@ -47,6 +47,7 @@ deny = [
 
 skip = [
   { name = "bitflags" },       # old 1.0 version via glutin, png, spirv, …
+  { name = "block2" },         # old version via glutin->icrate
   { name = "event-listener" }, # TODO(emilk): rustls pulls in two versions of this 😭
   { name = "libloading" },     # wgpu-hal itself depends on 0.8 while some of its dependencies, like ash and d3d12, depend on 0.7
   { name = "memoffset" },      # tiny dependency
@@ -61,7 +62,7 @@ skip = [
 skip-tree = [
   { name = "criterion" },     # dev-dependency
   { name = "fastrand" },      # old version via accesskit_unix
-  { name = "foreign-types" }, # small crate. Old version via cocoa and core-graphics (winit).
+  { name = "foreign-types" }, # small crate. Old version via core-graphics (winit).
   { name = "objc2" },         # old version via accesskit_macos
   { name = "polling" },       # old version via accesskit_unix
   { name = "rfd" },           # example dependency