Provide generic wxWebView::Find() implementation

This implementation is based on javascript 'window.find()'
https://developer.mozilla.org/en-US/docs/Web/API/Window/find
It's not standard, but implemented in most browsers.

It's not a complete implementation as it can't determine how
many search results can be found.

If the backends API provides a native find interface it should be
used instead of this implementation, but it's good fallback.

include/wx/webview.h

@@ -257,6 +257,7 @@ private:
     static wxStringWebViewFactoryMap::iterator FindFactory(const wxString &backend);
 
     bool m_showMenu;
+    wxString m_findText;
     static wxStringWebViewFactoryMap m_factoryMap;
 
     wxDECLARE_ABSTRACT_CLASS(wxWebView);

interface/wx/webview.h

@@ -317,7 +317,7 @@ public:
     <a href="https://docs.microsoft.com/en-us/microsoft-edge/hosting/webview2">Edge WebView2</a>.
     It is available for Windows 7 and newer.
     The following features are currently unsupported with this backend:
-    virtual filesystems, custom urls, find.
+    virtual filesystems, custom urls.
 
     This backend is not enabled by default, to build it follow these steps:
     - Visual Studio 2015, or newer, is required

src/common/webview.cpp

@@ -203,10 +203,23 @@ void wxWebView::SelectAll()
     RunScript("window.getSelection().selectAllChildren(document.body);");
 }
 
-long wxWebView::Find(const wxString& WXUNUSED(text), int WXUNUSED(flags))
+long wxWebView::Find(const wxString& text, int flags)
 {
-    // TODO: could probably be implemented by script
-    return -1;
+    if (text != m_findText)
+        ClearSelection();
+    m_findText = text;
+    wxString output;
+    RunScript(wxString::Format("window.find('%s', %s, %s, %s, %s)",
+        text,
+        (flags & wxWEBVIEW_FIND_MATCH_CASE) ? "true" : "false",
+        (flags & wxWEBVIEW_FIND_BACKWARDS) ? "true" : "false",
+        (flags & wxWEBVIEW_FIND_WRAP) ? "true" : "false",
+        (flags & wxWEBVIEW_FIND_ENTIRE_WORD) ? "true" : "false"
+        ), &output);
+    if (output.IsSameAs("false", false))
+        return wxNOT_FOUND;
+    else
+        return 1;
 }
 
 // static