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

xmodule/tests/test_utils_escape_html_characters.py

@@ -0,0 +1,63 @@
+"""Tests for methods defined in util/misc.py"""
+
+
+from unittest import TestCase
+
+from xmodule.util.misc import escape_html_characters
+
+
+class UtilHtmlEscapeTests(TestCase):
+    """
+    Tests for methods exposed in util/misc
+    """
+
+    final_content = " This is a paragraph. "
+
+    def test_escape_html_comments(self):
+        html_content = """
+            <!--This is a comment. Comments are not displayed in the browser-->
+
+            This is a paragraph.
+            """
+        assert escape_html_characters(html_content) == self.final_content
+
+    def test_escape_cdata_comments(self):
+        html_content = """
+            <![CDATA[
+                function matchwo(a,b)
+                {
+                if (a < b && a < 0) then
+                  {
+                  return 1;
+                  }
+                else
+                  {
+                  return 0;
+                  }
+                }
+            ]]>
+
+            This is a paragraph.
+            """
+        assert escape_html_characters(html_content) == self.final_content
+
+    def test_escape_non_breaking_space(self):
+        html_content = """
+            &nbsp;&nbsp;
+            &nbsp;
+            <![CDATA[
+                function matchwo(a,b)
+                {
+                if (a < b && a < 0) then
+                  {
+                  return 1;
+                  }
+                else
+                  {
+                  return 0;
+                  }
+                }
+            ]]>
+            This is a paragraph.&nbsp;
+        """
+        assert escape_html_characters(html_content) == self.final_content