apprt/gtk: set multiple content types for clipboard ops

This supports the new `setClipboard` parameter that may provide data in
multiple formats, allowing us to copy rich text to/from the clipboard as
well as other types in the future.

src/Surface.zig

@@ -1962,7 +1962,7 @@ fn copySelectionToClipboards(
 ) !void {
     // Create an arena to simplify memory management here.
     var arena = ArenaAllocator.init(self.alloc);
-    errdefer arena.deinit();
+    defer arena.deinit();
     const alloc = arena.allocator();
 
     // The options we'll use for all formatting. We'll just override the

src/apprt/gtk/class/surface.zig

@@ -3340,8 +3340,9 @@ const Clipboard = struct {
     ) void {
         const priv = self.private();
 
-        // For GTK, we only support text/plain type to set strings currently.
-        const val: [:0]const u8 = for (contents) |content| {
+        // Grab our plaintext content for use in confirmation dialogs
+        // and signals. We always expect one to exist.
+        const text: [:0]const u8 = for (contents) |content| {
             if (std.mem.eql(u8, content.mime, "text/plain")) {
                 break content.data;
             }
@@ -3353,12 +3354,32 @@ const Clipboard = struct {
                 priv.gl_area.as(gtk.Widget),
                 clipboard_type,
             ) orelse return;
-            clipboard.setText(val);
+
+            const alloc = Application.default().allocator();
+            if (alloc.alloc(*gdk.ContentProvider, contents.len)) |providers| {
+                // Note: we don't need to unref the individual providers
+                // because new_union takes ownership of them.
+                defer alloc.free(providers);
+
+                for (contents, 0..) |content, i| {
+                    const bytes = glib.Bytes.new(content.data.ptr, content.data.len);
+                    defer bytes.unref();
+                    const provider = gdk.ContentProvider.newForBytes(content.mime, bytes);
+                    providers[i] = provider;
+                }
+
+                const all = gdk.ContentProvider.newUnion(providers.ptr, providers.len);
+                defer all.unref();
+                _ = clipboard.setContent(all);
+            } else |_| {
+                // If we fail to alloc, we can at least set the text content.
+                clipboard.setText(text);
+            }
 
             Surface.signals.@"clipboard-write".impl.emit(
                 self,
                 null,
-                .{ clipboard_type, val.ptr },
+                .{ clipboard_type, text.ptr },
                 null,
             );
 
@@ -3368,7 +3389,7 @@ const Clipboard = struct {
         showClipboardConfirmation(
             self,
             .{ .osc_52_write = clipboard_type },
-            val,
+            text,
         );
     }