* Consolidates and renames the runtime used as a base for all the others:
* Before: `xmodule.x_module:DescriptorSystem` and
`xmodule.mako_block:MakoDescriptorSystem`.
* After: `xmodule.x_module:ModuleStoreRuntime`.
* Co-locates and renames the runtimes for importing course OLX:
* Before: `xmodule.x_module:XMLParsingSystem` and
`xmodule.modulestore.xml:ImportSystem`.
* After: `xmodule.modulestore.xml:XMLParsingModuleStoreRuntime` and
`xmodule.modulestore.xml:XMLImportingModuleStoreRuntime`.
* Note: I would have liked to consolidate these, but it would have
involved nontrivial test refactoring.
* Renames the stub Old Mongo runtime:
* Before: `xmodule.modulestore.mongo.base:CachingDescriptorSystem`.
* After: `xmodule.modulestore.mongo.base:OldModuleStoreRuntime`.
* Renames the Split Mongo runtime, the which is what runs courses in LMS and CMS:
* Before: `xmodule.modulestore.split_mongo.caching_descriptor_system:CachingDescriptorSystem`.
* After: `xmodule.modulestore.split_mongo.runtime:SplitModuleStoreRuntime`.
* Renames some of the dummy runtimes used only in unit tests.
Blockstore and all of its (experimental) functionality has been replaced with
openedx-learning, aka "Learning Core". This commit uninstalls the now-unused
openedx-blockstore package and removes all dangling references to it.
Note: This also removes the `copy_library_from_v1_to_v2` management command,
which has been broken ever since we switched from Blockstore to Learning Core.
Part of this DEPR: https://github.com/openedx/public-engineering/issues/238
* feat: tests for copying units in content_staging app
* chore: convert old tests to pytest style
* feat: make pasting units work (in Studio backend API)
* refactor: make XmlMixin.parse_xml more like standard XBlock behavior
