Bug 1851641 - Fix hiding cursor while typing. r=masayuki

This didn't work properly for non-native key bindings because:

  https://hg.mozilla.org/mozilla-central/rev/8934e6e6ccb6

Moved the DetachedFromEditorOrDefaultPrevented() check before the "hide
cursor" check, rather than after. This was a quick fix, because if we're
detached from the editor, then GetPresContext would assert. But I didn't
realize at the time (since it was a long time since I wrote the patch)
that most events there actually are default-prevented.

To fix this, split the checks. Checks for DetachedFromEditor() first,
and only after potentially hiding the cursor check whether the event is
default-prevented.

Differential Revision: https://phabricator.services.mozilla.com/D187536

editor/libeditor/EditorEventListener.cpp

@@ -643,10 +643,6 @@ nsresult EditorEventListener::KeyPress(WidgetKeyboardEvent* aKeyboardEvent) {
     return rv;
   }
 
-  if (DetachedFromEditorOrDefaultPrevented(aKeyboardEvent)) {
-    return NS_OK;
-  }
-
   auto GetWidget = [&]() -> nsIWidget* {
     if (aKeyboardEvent->mWidget) {
       return aKeyboardEvent->mWidget;
@@ -659,6 +655,10 @@ nsresult EditorEventListener::KeyPress(WidgetKeyboardEvent* aKeyboardEvent) {
     return presContext->GetTextInputHandlingWidget();
   };
 
+  if (DetachedFromEditor()) {
+    return NS_OK;
+  }
+
   if (LookAndFeel::GetInt(LookAndFeel::IntID::HideCursorWhileTyping)) {
     if (nsPresContext* pc = GetPresContext()) {
       if (nsIWidget* widget = GetWidget()) {
@@ -667,6 +667,10 @@ nsresult EditorEventListener::KeyPress(WidgetKeyboardEvent* aKeyboardEvent) {
     }
   }
 
+  if (aKeyboardEvent->DefaultPrevented()) {
+    return NS_OK;
+  }
+
   if (!ShouldHandleNativeKeyBindings(aKeyboardEvent)) {
     return NS_OK;
   }