Bug 1729358 - Part 1: Move FocusState to TextControlElement; r=smaug

And convert FocusTristate to enum class.

Differential Revision: https://phabricator.services.mozilla.com/D124693

dom/html/HTMLTextAreaElement.cpp

@@ -135,7 +135,7 @@ nsresult HTMLTextAreaElement::Clone(dom::NodeInfo* aNodeInfo,
 // nsIContent
 
 void HTMLTextAreaElement::Select() {
-  if (FocusState() != eUnfocusable) {
+  if (FocusState() != FocusTristate::eUnfocusable) {
     if (RefPtr<nsFocusManager> fm = nsFocusManager::GetFocusManager()) {
       fm->SetFocus(this, nsIFocusManager::FLAG_NOSCROLL);
     }