refactor: move xmodule folder to root

- Moving xmodule folder to root as we're dissolving sub-projects of common folder in edx-platform
    - More info: https://openedx.atlassian.net/browse/BOM-2579
- -e common/lib/xmodule has been removed from the requirements as xmodule has itself become the part of edx-platform and not being installed through requirements
- The test files common/lib/xmodule/test_files/ have been removed as they are not being used anymore

.github/workflows/pylint-checks.yml

@@ -26,6 +26,8 @@ jobs:
             path: "common"
           - module-name: cms
             path: "cms"
+          - module-name: xmodule
+            path: "xmodule"
 
 
     name: pylint ${{ matrix.module-name }}

.github/workflows/unit-test-shards.json

@@ -270,5 +270,11 @@
     "paths": [
       "common/djangoapps/"
     ]
+  },
+  "xmodule-1": {
+    "settings": "lms.envs.test",
+    "paths": [
+      "xmodule/"
+    ]
   }
 }

.github/workflows/unit-tests.yml

@@ -32,6 +32,7 @@ jobs:
             "common-1",
             "common-2",
             "common-3",
+            "xmodule-1"
         ]