Re-add @private, undocumented .identifier method that was only me… (#2109)

* Re-add `@private`, undocumented `.identifier` method that was only meant for internal framework use but was used by some downstream consumers. This method will be removed in a coming minor release.

* add nocov marks

Author: joelhawksley

docs/CHANGELOG.md

@@ -10,6 +10,10 @@ nav_order: 5
 
 ## main
 
+* Re-add `@private`, undocumented `.identifier` method that was only meant for internal framework use but was used by some downstream consumers. This method will be removed in a coming minor release.
+
+    *Joel Hawksley*
+
 ## 3.15.0
 
 * Add basic internal testing for memory allocations.

lib/view_component/base.rb

@@ -574,6 +574,15 @@ def compiler
         @__vc_compiler ||= Compiler.new(self)
       end
 
+      # @private
+      def identifier
+        # :nocov:
+        Kernel.warn("WARNING: The #{self.class}.identifier is undocumented and was meant for internal framework usage only. As it is no longer used by the framework it will be removed in a coming non-breaking ViewComponent release.")
+
+        source_location
+        # :nocov:
+      end
+
       # Set the parameter name used when rendering elements of a collection ([documentation](/guide/collections)):
       #
       # ```ruby