LibWeb/HTML: Implement inner text set according to spec

Replaced the ad-hoc implementation with a spec compliant one.
This change fixes 36 WPT tests.

Tests/LibWeb/Text/expected/HTML/set-innerText.txt

@@ -0,0 +1,3 @@
+Empty string: ""
+Simple text: "foo"
+Text with newlines: "<br>foo<br>bar<br>baz<br><br>foobar<br>"

Tests/LibWeb/Text/input/HTML/set-innerText.html

@@ -0,0 +1,12 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        let element = document.createElement('div');
+        element.innerText = "";
+        println('Empty string: "' + element.innerHTML + '"');
+        element.innerText = "foo";
+        println('Simple text: "' + element.innerHTML + '"');
+        element.innerText = "\rfoo\nbar\r\nbaz\n\rfoobar\n";
+        println('Text with newlines: "' + element.innerHTML + '"');
+    });
+</script>

Userland/Libraries/LibWeb/HTML/HTMLElement.cpp

@@ -9,6 +9,7 @@
 #include <LibWeb/Bindings/ExceptionOrUtils.h>
 #include <LibWeb/Bindings/HTMLElementPrototype.h>
 #include <LibWeb/DOM/Document.h>
+#include <LibWeb/DOM/ElementFactory.h>
 #include <LibWeb/DOM/IDLEventListener.h>
 #include <LibWeb/DOM/LiveNodeList.h>
 #include <LibWeb/DOM/ShadowRoot.h>
@@ -32,6 +33,7 @@
 #include <LibWeb/Layout/Box.h>
 #include <LibWeb/Layout/BreakNode.h>
 #include <LibWeb/Layout/TextNode.h>
+#include <LibWeb/Namespace.h>
 #include <LibWeb/Painting/PaintableBox.h>
 #include <LibWeb/UIEvents/EventNames.h>
 #include <LibWeb/UIEvents/FocusEvent.h>
@@ -150,10 +152,13 @@ WebIDL::ExceptionOr<void> HTMLElement::set_content_editable(StringView content_e
     return WebIDL::SyntaxError::create(realm(), "Invalid contentEditable value, must be 'true', 'false', or 'inherit'"_string);
 }
 
+// https://html.spec.whatwg.org/multipage/dom.html#set-the-inner-text-steps
 void HTMLElement::set_inner_text(StringView text)
 {
+    // 1. Let fragment be the rendered text fragment for value given element's node document.
+    // 2. Replace all with fragment within element.
     remove_all_children();
-    MUST(append_child(document().create_text_node(MUST(String::from_utf8(text)))));
+    append_rendered_text_fragment(text);
 
     set_needs_style_update(true);
 }
@@ -165,6 +170,45 @@ WebIDL::ExceptionOr<void> HTMLElement::set_outer_text(String)
     return {};
 }
 
+// https://html.spec.whatwg.org/multipage/dom.html#rendered-text-fragment
+void HTMLElement::append_rendered_text_fragment(StringView input)
+{
+    // FIXME: 1. Let fragment be a new DocumentFragment whose node document is document.
+    //      Instead of creating a DocumentFragment the nodes are appended directly.
+
+    // 2. Let position be a position variable for input, initially pointing at the start of input.
+    // 3. Let text be the empty string.
+    // 4. While position is not past the end of input:
+    while (!input.is_empty()) {
+        // 1. Collect a sequence of code points that are not U+000A LF or U+000D CR from input given position, and set text to the result.
+        auto newline_index = input.find_any_of("\n\r"sv);
+        size_t const sequence_end_index = newline_index.value_or(input.length());
+        StringView const text = input.substring_view(0, sequence_end_index);
+        input = input.substring_view_starting_after_substring(text);
+
+        // 2. If text is not the empty string, then append a new Text node whose data is text and node document is document to fragment.
+        if (!text.is_empty()) {
+            MUST(append_child(document().create_text_node(MUST(String::from_utf8(text)))));
+        }
+
+        // 3. While position is not past the end of input, and the code point at position is either U+000A LF or U+000D CR:
+        while (input.starts_with('\n') || input.starts_with('\r')) {
+            // 1. If the code point at position is U+000D CR and the next code point is U+000A LF, then advance position to the next code point in input.
+            if (input.starts_with("\r\n"sv)) {
+                // 2. Advance position to the next code point in input.
+                input = input.substring_view(2);
+            } else {
+                // 2. Advance position to the next code point in input.
+                input = input.substring_view(1);
+            }
+
+            // 3. Append the result of creating an element given document, br, and the HTML namespace to fragment.
+            auto br_element = DOM::create_element(document(), HTML::TagNames::br, Namespace::HTML).release_value();
+            MUST(append_child(br_element));
+        }
+    }
+}
+
 // https://html.spec.whatwg.org/multipage/dom.html#get-the-text-steps
 String HTMLElement::get_the_text_steps()
 {

Userland/Libraries/LibWeb/HTML/HTMLElement.h

@@ -97,6 +97,7 @@ private:
     virtual void did_receive_focus() override;
 
     [[nodiscard]] String get_the_text_steps();
+    void append_rendered_text_fragment(StringView input);
 
     JS::GCPtr<DOMStringMap> m_dataset;