Vendor dependencies for 0.3.0 release

vendor/accesskit/README.md

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+# AccessKit
+
+This is the shared cross-platform crate for [AccessKit](https://accesskit.dev/). It defines the data structures that represent an accessibility tree, and the trait for handling action requests from assistive technologies.
+
+To use AccessKit in your application or toolkit, you will also need a platform adapter. The following platform adapters are currently available:
+
+* [accesskit_windows](https://crates.io/crates/accesskit_windows): exposes an AccessKit tree on Windows using the UI Automation API
+* [accesskit_macos](https://crates.io/crates/accesskit_macos): exposes an AccessKit tree on MacOS through the Cocoa `NSAccessibility` protocol
+* [accesskit_unix](https://crates.io/crates/accesskit_unix): exposes an AccessKit tree on Linux and Unix systems through the AT-SPI protocol
+* [accesskit_android](https://crates.io/crates/accesskit_android): exposes an AccessKit tree on Android through the Java-based Android accessibility API
+* [accesskit_winit](https://crates.io/crates/accesskit_winit): wraps other platform adapters for use with the [winit](https://crates.io/crates/winit) windowing library
+
+Some platform adapters include simple examples.