Match User method in TeamMember (#11861)

I'm not sure why this doesn't match, but it's confusing to work with in
some templates that sometimes list `TeamMember` and other times list
`User` instances. Instead, just match these methods so it's always the
same.

- Refs readthedocs/ext-theme#546

Author: agjohnson

readthedocs/organizations/models.py

@@ -401,13 +401,22 @@ def username(self):
 
         return "Unknown"
 
-    @property
-    def full_name(self):
+    def get_full_name(self):
         """Return member or invite full name."""
         if self.is_member:
             return self.member.get_full_name()
         return ""
 
+    @property
+    def full_name(self):
+        """
+        Alias property for `get_full_name`.
+
+        This is deprecated, use `get_full_name` as it matches the underlying
+        :py:method:`User.get_full_name`.
+        """
+        return self.get_full_name()
+
     @property
     def email(self):
         """Return member or invite email address."""