feat: Paste Components (OLX) into any Unit in Studio (#31969)

* feat: Implement paste button

* chore: improve docs and add tests for python API

* fix: drive-by fix to use a better API for comparing XML

* feat: track which XBlock something was copied from

* feat: add tests

* feat: enable import linter so content_staging's public API is respected

* fix: error seen when trying to paste drag-and-drop-v2 blocks

* fix: use strip_text=True consistently for XML comparisons

* refactor: rename get_user_clipboard_status to get_user_clipboard

* feat: Better error reporting when pasting in Studio

* chore: convert new test suite to pytest assertions

* refactor: push READY status check into the API per review suggestion

* fix: use strip_text=True consistently for XML comparisons

* fix: store "copied_from_block" as a string to avoid Reference field issues

* fix: minor lint error

* refactor: move data types to data.py per OEP-49

cms/lib/xblock/authoring_mixin.py

@@ -8,6 +8,7 @@ import logging
 from django.conf import settings
 from web_fragments.fragment import Fragment
 from xblock.core import XBlock, XBlockMixin
+from xblock.fields import String, Scope
 
 log = logging.getLogger(__name__)
 
@@ -43,3 +44,10 @@ class AuthoringMixin(XBlockMixin):
         fragment.add_javascript_url(self._get_studio_resource_url('/js/xblock/authoring.js'))
         fragment.initialize_js('VisibilityEditorInit')
         return fragment
+
+    copied_from_block = String(
+        # Note: used by the content_staging app. This field is not needed in the LMS.
+        help="ID of the block that this one was copied from, if any. Used when copying and pasting blocks in Studio.",
+        scope=Scope.settings,
+        enforce_type=True,
+    )