widget: Provide a way to copy the selection to clipboard as HTML

Currently, copying to HTML is disabled (#if 0) in the code, because
it will generate the potentially huge selection data in both text and
HTML formats.

Instead, provide API to tell vte which format to use.

https://bugzilla.gnome.org/show_bug.cgi?id=365121

bindings/vala/app.ui

@@ -43,6 +43,7 @@
             <property name="receives_default">True</property>
             <property name="tooltip_text" translatable="yes">Copy</property>
             <property name="action_name">win.copy</property>
+            <property name="action_target">"text"</property>
             <property name="focus_on_click">False</property>
             <child>
               <object class="GtkImage" id="image2">

bindings/vala/app.vala

@@ -196,7 +196,7 @@ class Window : Gtk.ApplicationWindow
   };
 
   private const GLib.ActionEntry[] action_entries = {
-    { "copy",        action_copy_cb            },
+    { "copy",        action_copy_cb,       "s" },
     { "copy-match",  action_copy_match_cb, "s" },
     { "paste",       action_paste_cb           },
     { "reset",       action_reset_cb,      "b" },
@@ -564,9 +564,12 @@ class Window : Gtk.ApplicationWindow
 
   /* Callbacks */
 
-  private void action_copy_cb()
+  private void action_copy_cb(GLib.SimpleAction action, GLib.Variant? parameter)
   {
-    terminal.copy_clipboard();
+    size_t len;
+    unowned string str = parameter.get_string(out len);
+
+    terminal.copy_clipboard_format(str == "html" ? Vte.Format.HTML : Vte.Format.TEXT);
   }
 
   private void action_copy_match_cb(GLib.SimpleAction action, GLib.Variant? parameter)
@@ -625,7 +628,8 @@ class Window : Gtk.ApplicationWindow
       return false;
 
     var menu = new GLib.Menu();
-    menu.append("_Copy", "win.copy");
+    menu.append("_Copy", "win.copy::text");
+    menu.append("Copy As _HTML", "win.copy::html");
 
 #if VALA_0_24
     if (event != null) {

doc/reference/vte-sections.txt

@@ -5,6 +5,7 @@ VteTerminal
 VteCursorBlinkMode
 VteCursorShape
 VteEraseBinding
+VteFormat
 VteWriteFlags
 VteSelectionFunc
 vte_terminal_new
@@ -13,7 +14,7 @@ vte_terminal_feed_child
 vte_terminal_feed_child_binary
 vte_terminal_select_all
 vte_terminal_unselect_all
-vte_terminal_copy_clipboard
+vte_terminal_copy_clipboard_format
 vte_terminal_paste_clipboard
 vte_terminal_copy_primary
 vte_terminal_paste_primary
@@ -102,6 +103,8 @@ VTE_TYPE_CURSOR_SHAPE
 vte_cursor_shape_get_type
 VTE_TYPE_ERASE_BINDING
 vte_erase_binding_get_type
+VTE_TYPE_FORMAT
+vte_format_get_type
 VTE_TYPE_WRITE_FLAGS
 vte_write_flags_get_type
 VTE_TYPE_TERMINAL
@@ -123,6 +126,7 @@ vte_terminal_get_current_directory_uri
 vte_terminal_get_current_file_uri
 
 <SUBSECTION Deprecated>
+vte_terminal_copy_clipboard
 vte_terminal_match_set_cursor
 vte_terminal_match_add_gregex
 vte_terminal_search_get_gregex