base64 functions must be given byte strings

The base64 stdlib functions require byte strings.  So we have to
transform the strings into bytes before handing to the stdlib and then
transform them back into text before handing back to ansible.

Fixes #22873

(cherry picked from commit 589e217278)

lib/ansible/plugins/filter/core.py

@@ -459,6 +459,14 @@ def do_groupby(environment, value, attribute):
     return [tuple(t) for t in _do_groupby(environment, value, attribute)]
 
 
+def b64encode(string):
+    return to_text(base64.b64encode(to_bytes(string, errors='surrogate_then_strict')))
+
+
+def b64decode(string):
+    return to_text(base64.b64decode(to_bytes(string, errors='surrogate_then_strict')))
+
+
 class FilterModule(object):
     ''' Ansible core jinja2 filters '''
 
@@ -468,8 +476,8 @@ class FilterModule(object):
             'groupby': do_groupby,
 
             # base 64
-            'b64decode': partial(unicode_wrap, base64.b64decode),
-            'b64encode': partial(unicode_wrap, base64.b64encode),
+            'b64decode': b64decode,
+            'b64encode': b64encode,
 
             # uuid
             'to_uuid': to_uuid,