dom: Add the attribute mutation reason (#40527)

For some specific cases (one of them see below) where are requirement to
identify the reason of the attribute mutation (by whom/why it was
changed - by cloning, parser or directly), so the following `reason`
parameter was added to `AttributeMutation::Set` option.

Note that for the HTMLMediaElement the internal `muted` state should be
set to true when the element is created and the element has a `muted`
content attribute specified (should be done once on the first attribute
mutation caused by parser or cloning).

See https://html.spec.whatwg.org/multipage/#dom-media-muted

Testing: Improvements in the following tests
-
html/semantics/embedded-content/media-elements/user-interface/muted.html

Signed-off-by: Andrei Volykhin <andrei.volykhin@gmail.com>

components/script/dom/html/htmltextareaelement.rs

@@ -526,7 +526,7 @@ impl VirtualMethods for HTMLTextAreaElement {
             local_name!("disabled") => {
                 let el = self.upcast::<Element>();
                 match mutation {
-                    AttributeMutation::Set(_) => {
+                    AttributeMutation::Set(..) => {
                         el.set_disabled_state(true);
                         el.set_enabled_state(false);
 
@@ -572,7 +572,7 @@ impl VirtualMethods for HTMLTextAreaElement {
                 {
                     let mut placeholder = self.placeholder.borrow_mut();
                     placeholder.clear();
-                    if let AttributeMutation::Set(_) = mutation {
+                    if let AttributeMutation::Set(..) = mutation {
                         placeholder.push_str(attr.value().as_ref());
                     }
                 }
@@ -581,7 +581,7 @@ impl VirtualMethods for HTMLTextAreaElement {
             local_name!("readonly") => {
                 let el = self.upcast::<Element>();
                 match mutation {
-                    AttributeMutation::Set(_) => {
+                    AttributeMutation::Set(..) => {
                         el.set_read_write_state(false);
                     },
                     AttributeMutation::Removed => {