Correctly handle setting textContent to empty for DocFrag and Element

Fixes an [non-critical] error on old.reddit.com

src/browser/tests/document_fragment/document_fragment.html

@@ -176,3 +176,16 @@
   testing.expectEqual("Nested content", clonedInner.textContent);
 }
 </script>
+
+<script id=textContent>
+{
+  const df = document.createDocumentFragment();
+  df.appendChild(document.createElement("div"));
+  testing.expectEqual(1, df.childNodes.length);
+  df.textContent = '';
+  testing.expectEqual(0, df.childNodes.length);
+
+  df.textContent = ' ';
+  testing.expectEqual(1, df.childNodes.length);
+}
+</script>

src/browser/tests/element/element.html

@@ -153,3 +153,16 @@
   testing.expectEqual(d, parent.childNodes[3]);
 }
 </script>
+
+<script id=textContent>
+{
+  const parent = document.createElement('div');
+  parent.appendChild(document.createElement('div'));
+  testing.expectEqual(1, parent.childNodes.length);
+  parent.textContent = '';
+  testing.expectEqual(0, parent.childNodes.length);
+
+  parent.textContent = ' ';
+  testing.expectEqual(1, parent.childNodes.length);
+}
+</script>

src/browser/webapi/Node.zig

@@ -269,11 +269,21 @@ pub fn getTextContentAlloc(self: *Node, allocator: Allocator) error{WriteFailed}
 
 pub fn setTextContent(self: *Node, data: []const u8, page: *Page) !void {
     switch (self._type) {
-        .element => |el| return el.replaceChildren(&.{.{ .text = data }}, page),
+        .element => |el| {
+            if (data.len == 0) {
+                return el.replaceChildren(&.{}, page);
+            }
+            return el.replaceChildren(&.{.{ .text = data }}, page);
+        },
         .cdata => |c| c._data = try page.arena.dupe(u8, data),
         .document => {},
         .document_type => {},
-        .document_fragment => |frag| return frag.replaceChildren(&.{.{ .text = data }}, page),
+        .document_fragment => |frag| {
+            if (data.len == 0) {
+                return frag.replaceChildren(&.{}, page);
+            }
+            return frag.replaceChildren(&.{.{ .text = data }}, page);
+        },
         .attribute => |attr| return attr.setValue(data, page),
     }
 }