Add Android popup support; add popupNavigate event for both platforms

[modos189]

Android

Introduces PopupWebChromeClient - a delegating wrapper around the existing WebChromeClient that intercepts onCreateWindow and presents the popup in a bottom-sheet-style Dialog. BottomSheetDialog (Material Components) was intentionally avoided to preserve the project's stated Android 19+ support; swipe-to-dismiss is implemented manually using VelocityTracker and touch event interception on both the toolbar and the WebView content area (when scrolled to top). The popup WebView inherits the parent's user-agent string.

target="_blank" links opened from inside an already-open popup are forwarded to the system browser rather than nesting another sheet.

A new optional createWebChromeClient factory is added alongside the existing createWebViewClient, using the same (webview, clientClass) => Client pattern.

iOS

A WKNavigationDelegate is attached to the popup WKWebView so that navigation events are now surfaced through the shared popupNavigate event, consistent with Android.

New API

name	description
supportPopups	Now works on Android in addition to iOS. Defaults to true.
popupNavigate event	Fired on every navigation inside the popup. Set args.cancel = true to close it and handle the URL in app code.
createWebChromeClient	Android: optional factory to provide a custom WebChromeClient, same pattern as createWebViewClient.