LibWeb: Use correct IDL for HTTPFormElement's method attribute

Removed the custom getter and updated the idl so that the attribute
is Reflected and Enumerated.

Tests/LibWeb/Text/expected/form-method-attribute.txt

@@ -0,0 +1,51 @@
+form: unset
+form.getAttribute('method') == 'null'
+form.method == 'get'
+
+form.setAttribute('method', '')
+form.getAttribute('method') == ''
+form.method == 'get'
+
+form.setAttribute('method', 'undefined')
+form.getAttribute('method') == 'undefined'
+form.method == 'get'
+
+form.setAttribute('method', 'null')
+form.getAttribute('method') == 'null'
+form.method == 'get'
+
+form.setAttribute('method', 'get')
+form.getAttribute('method') == 'get'
+form.method == 'get'
+
+form.setAttribute('method', 'post')
+form.getAttribute('method') == 'post'
+form.method == 'post'
+
+form.setAttribute('method', 'dialog')
+form.getAttribute('method') == 'dialog'
+form.method == 'dialog'
+
+form.setAttribute('method', 'GeT')
+form.getAttribute('method') == 'GeT'
+form.method == 'get'
+
+form.setAttribute('method', 'POST')
+form.getAttribute('method') == 'POST'
+form.method == 'post'
+
+form.setAttribute('method', 'DIAlog')
+form.getAttribute('method') == 'DIAlog'
+form.method == 'dialog'
+
+form.setAttribute('method', 'foo')
+form.getAttribute('method') == 'foo'
+form.method == 'get'
+
+form.setAttribute('method', 'xpost')
+form.getAttribute('method') == 'xpost'
+form.method == 'get'
+
+form.setAttribute('method', '5%')
+form.getAttribute('method') == '5%'
+form.method == 'get'

Tests/LibWeb/Text/input/form-method-attribute.html

@@ -0,0 +1,23 @@
+<script src="./include.js"></script>
+<script>
+    test(() => {
+        const form = document.createElement('form');
+        const values = [
+            '', undefined, null,
+            'get', 'post', 'dialog',
+            'GeT', 'POST', 'DIAlog',
+            'foo', 'xpost', '5%'
+        ];
+
+        println('form: unset');
+        println(`form.getAttribute('method') == '${form.getAttribute('method')}'`);
+        println(`form.method == '${form.method}'`);
+        for (value of values) {
+            form.setAttribute('method', value);
+            println('');
+            println(`form.setAttribute('method', '${value}')`);
+            println(`form.getAttribute('method') == '${form.getAttribute('method')}'`);
+            println(`form.method == '${form.method}'`);
+        }
+    });
+</script>

Userland/Libraries/LibWeb/HTML/HTMLFormElement.cpp

@@ -565,23 +565,6 @@ Vector<JS::NonnullGCPtr<DOM::Element>> HTMLFormElement::get_submittable_elements
     return submittable_elements;
 }
 
-// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#dom-fs-method
-StringView HTMLFormElement::method() const
-{
-    // The method and enctype IDL attributes must reflect the respective content attributes of the same name, limited to only known values.
-    // FIXME: This should probably be `Reflect` in the IDL.
-    auto method_state = method_state_from_form_element(*this);
-    switch (method_state) {
-    case MethodAttributeState::GET:
-        return "get"sv;
-    case MethodAttributeState::POST:
-        return "post"sv;
-    case MethodAttributeState::Dialog:
-        return "dialog"sv;
-    }
-    VERIFY_NOT_REACHED();
-}
-
 // https://html.spec.whatwg.org/multipage/forms.html#dom-form-rellist
 JS::NonnullGCPtr<DOM::DOMTokenList> HTMLFormElement::rel_list()
 {

Userland/Libraries/LibWeb/HTML/HTMLFormElement.h

@@ -88,7 +88,6 @@ public:
     bool constructing_entry_list() const { return m_constructing_entry_list; }
     void set_constructing_entry_list(bool value) { m_constructing_entry_list = value; }
 
-    StringView method() const;
     WebIDL::ExceptionOr<void> set_method(String const&);
 
     JS::NonnullGCPtr<DOM::DOMTokenList> rel_list();

Userland/Libraries/LibWeb/HTML/HTMLFormElement.idl

@@ -16,6 +16,14 @@ enum EnctypeAttribute {
     "text/plain"
 };
 
+// https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#attr-fs-method
+[MissingValueDefault=get, InvalidValueDefault=get]
+enum MethodAttribute {
+    "get",
+    "post",
+    "dialog"
+};
+
 // https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#selectionmode
 enum SelectionMode {
     "select",
@@ -35,7 +43,7 @@ interface HTMLFormElement : HTMLElement {
     [CEReactions, Enumerated=Autocomplete, Reflect] attribute DOMString autocomplete;
     [CEReactions, Enumerated=EnctypeAttribute, Reflect] attribute DOMString enctype;
     [CEReactions, Enumerated=EnctypeAttribute, Reflect=enctype] attribute DOMString encoding;
-    [CEReactions] attribute DOMString method;
+    [CEReactions, Enumerated=MethodAttribute, Reflect] attribute DOMString method;
     [CEReactions, Reflect] attribute DOMString name;
     [CEReactions, Reflect=novalidate] attribute boolean noValidate;
     [CEReactions, Reflect] attribute DOMString target;