Fix bug (#18355) where encrypted inventories fail 18355 (#18373)

* Fix bug (#18355) where encrypted inventories fail

This is first part of fix for #18355
* Make DataLoader._get_file_contents return bytes

The issue #18355 is caused by a change to inventory to
stop using _get_file_contents so that it can handle text
encoding itself to better protect against harmless text
encoding errors in ini files (invalid unicode text in
comment fields).

So this makes _get_file_contents return bytes so it and other
callers can handle the to_text().

The data returned by _get_file_contents() is now a bytes object
instead of a text object. The callers of _get_file_contents() have
been updated to call to_text() themselves on the results.

Previously, the ini parser attempted to work around
ini files that potentially include non-vailid unicode
in comment lines. To do this, it stopped using
DataLoader._get_file_contents() which does the decryption of
files if vault encrypted. It didn't use that because _get_file_contents
previously did to_text() on the read data itself.

_get_file_contents() returns a bytestring now, so ini.py
can call it and still special case ini file comments when
converting to_text(). That also means encrypted inventory files
are decrypted first.

Fixes #18355

test/units/mock/loader.py

@@ -23,6 +23,8 @@ import os
 
 from ansible.errors import AnsibleParserError
 from ansible.parsing.dataloader import DataLoader
+from ansible.module_utils._text import to_bytes
+
 
 class DictDataLoader(DataLoader):
 
@@ -39,9 +41,11 @@ class DictDataLoader(DataLoader):
             return self.load(self._file_mapping[path], path)
         return None
 
+    # TODO: the real _get_file_contents returns a bytestring, so we actually convert the
+    #       unicode/text it's created with to utf-8
     def _get_file_contents(self, path):
         if path in self._file_mapping:
-            return (self._file_mapping[path], False)
+            return (to_bytes(self._file_mapping[path]), False)
         else:
             raise AnsibleParserError("file not found: %s" % path)