Notify properties on deletion in PasswordEntryBuffer
The GtkEntryBufferClass.deleted_text() behaviour changed between GTK3 and GTK4, which means any subclass of GtkEntryBuffer is now responsible for emitting the "notify" signal for the "text" and "length" properties.
Without this, the GtkText delegate widget used by GtkPasswordEntry would not be able to communicate changes in the contents of its buffer.
Fixes: #3484 (closed)