Add proxy support (desktop only)

[bommbomm34]

Proxy support on Desktop

This pull request enables HTTP and SOCKS5 proxy support for desktop platforms (Windows, macOS and Linux). Android only supports a global proxy setting for all WebViews with ProxyController and iOS with WKWebView doesn't seem to support it at all. I tested this change only on Linux.

Changes

• Add docs
• Add proxy option to demo app

Public API

• Add jvmProxyConfig parameter to WryWebViewPanel. This change could be potentially breaking.
• Add proxyConfig to PlatformWebSettings.DesktopWebSettings
• Add proxyConfig to WebViewFactoryParam
• Add ProxyConfig
• Add JvmProxyConfig

Internal API

• Add proxy option to create_webview_with_user_agent, create_webview and create_webview_inner in Rust
• Update NativeBindings
• Some internal helper methods in Rust and Kotlin

Note

I don't know why there is a seperate create_webview_with_user_agent method. I didn't make a seperate method for proxy config like create_webview_with_proxy_config.