Report detailed error when internal remote functions fail

This is a redesign in how plugins call _remote_checksum().

- _remote_stat() has been modified to report the real error as
  AnsiblError
- Action plugin **unarchive** calls _remote_stat() directly instead of
   _remote_checksum()
- Action plugin **unarchive** also handles the exceptions directly
- Ensure get_exception() returns native text

Two other action plugins, **template** and **fetch**, also do a remote checksum.
In **template** we already call _remote_stat(), just like we now do for
unarchive, in **fetch** we do call _remote_checksum() and we make the
exact same mistake as the unarchive plugin. So that one could use a
redesign as well.

This fixes #19494

Before:
```
[dag@moria ansible.testing]$ ansible-playbook -v test137.yml
Using /home/dag/home-made/ansible.testing/ansible.cfg as config file

PLAY [localhost]
******************************************************************************************************

TASK [unarchive]
******************************************************************************************************
fatal: [localhost]: FAILED! => {"changed": false, "failed": true, "msg":
"python isn't present on the system.  Unable to compute checksum"}

PLAY RECAP
******************************************************************************************************
localhost                  : ok=0    changed=0    unreachable=0
failed=1
```

After:
```
[dag@moria ansible.testing]$ ansible-playbook -v test137.yml
Using /home/dag/home-made/ansible.testing/ansible.cfg as config file

PLAY [localhost]
*************************************************************************************************************

TASK [unarchive]
*************************************************************************************************************
fatal: [localhost]: FAILED! => {"changed": false, "failed": true, "msg":
"Failed to get information on remote file (/tmp/): sudo: unknown user:
foobar\nsudo: unable to initialize policy plugin\n"}

PLAY RECAP
*******************************************************************************************************************
localhost                  : ok=0    changed=0    unreachable=0
failed=1
```

lib/ansible/plugins/action/template.py

@@ -25,6 +25,7 @@ import time
 from ansible import constants as C
 from ansible.errors import AnsibleError
 from ansible.module_utils._text import to_bytes, to_native, to_text
+from ansible.module_utils.pycompat24 import get_exception
 from ansible.plugins.action import ActionBase
 from ansible.utils.hashing import checksum_s
 
@@ -43,8 +44,8 @@ class ActionModule(ActionBase):
                 dest = os.path.join(dest, base)
                 dest_stat = self._execute_remote_stat(dest, all_vars=all_vars, follow=False, tmp=tmp)
 
-        except Exception as e:
-            return dict(failed=True, msg=to_bytes(e))
+        except AnsibleError:
+            return dict(failed=True, msg=to_native(get_exception()))
 
         return dest_stat['checksum']
 
@@ -69,9 +70,9 @@ class ActionModule(ActionBase):
         else:
             try:
                 source = self._find_needle('templates', source)
-            except AnsibleError as e:
+            except AnsibleError:
                 result['failed'] = True
-                result['msg'] = to_native(e)
+                result['msg'] = to_native(get_exception())
 
         if 'failed' in result:
             return result