LibWeb: Implement input/textarea selection APIs

For both types of elements, `.selectionStart`, `.selectionEnd`,
`.selectionDirection`, `.setSelectionRange()`, `.select()` and the
`select` event are now implemented.

Tests/LibWeb/Text/expected/DOM/FormAssociatedElement-selection.txt

@@ -0,0 +1,24 @@
+Well hello friends  some
+text   text-input selectionStart: 0
+text-input selectionEnd: 0
+text-input selectionDirection: none
+date-input selectionStart: null
+date-input selectionEnd: null
+date-input selectionDirection: none
+textarea selectionStart: 0
+textarea selectionEnd: 0
+textarea selectionDirection: none
+text-input selectionStart: 18
+text-input selectionEnd: 18
+text-input selectionDirection: none
+date input setting selectionStart error: InvalidStateError: setSelectionStart does not apply to this input type
+text-input selectionStart: 0
+text-input selectionEnd: 18
+text-input selectionDirection: none
+text-input selectionStart: 2
+text-input selectionEnd: 4
+text-input selectionDirection: forward
+textarea selectionStart: 0
+textarea selectionEnd: 9
+textarea selectionDirection: none
+select event fired: 2 4

Tests/LibWeb/Text/input/DOM/FormAssociatedElement-selection.html

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+<input type="text" id="text-input">
+<input type="date" id="date-input">
+<textarea id="textarea">some
+text</textarea>
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        let textInput = document.getElementById('text-input');
+        let dateInput = document.getElementById('date-input');
+        let textarea = document.getElementById('textarea');
+
+        const dumpSelection = (element) => {
+            println(`${element.id} selectionStart: ${element.selectionStart}`);
+            println(`${element.id} selectionEnd: ${element.selectionEnd}`);
+            println(`${element.id} selectionDirection: ${element.selectionDirection}`);
+        };
+
+        dumpSelection(textInput);
+        dumpSelection(dateInput);
+        dumpSelection(textarea);
+
+        textInput.value = 'Well hello friends';
+        dumpSelection(textInput);
+
+        try {
+            dateInput.selectionStart = 0;
+        } catch (e) {
+            println(`date input setting selectionStart error: ${e}`);
+        }
+
+        textInput.addEventListener('select', e => println(`select event fired: ${e.target.selectionStart} ${e.target.selectionEnd}`))
+        textInput.select();
+        dumpSelection(textInput);
+        textInput.setSelectionRange(2, 4, 'forward');
+        dumpSelection(textInput);
+
+        textarea.select();
+        dumpSelection(textarea);
+    });
+</script>