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/parsing/test_data_loader.py

@@ -37,13 +37,13 @@ class TestDataLoader(unittest.TestCase):
 
     @patch.object(DataLoader, '_get_file_contents')
     def test_parse_json_from_file(self, mock_def):
-        mock_def.return_value = ("""{"a": 1, "b": 2, "c": 3}""", True)
+        mock_def.return_value = (b"""{"a": 1, "b": 2, "c": 3}""", True)
         output = self._loader.load_from_file('dummy_json.txt')
         self.assertEqual(output, dict(a=1,b=2,c=3))
 
     @patch.object(DataLoader, '_get_file_contents')
     def test_parse_yaml_from_file(self, mock_def):
-        mock_def.return_value = ("""
+        mock_def.return_value = (b"""
         a: 1
         b: 2
         c: 3
@@ -53,7 +53,7 @@ class TestDataLoader(unittest.TestCase):
 
     @patch.object(DataLoader, '_get_file_contents')
     def test_parse_fail_from_file(self, mock_def):
-        mock_def.return_value = ("""
+        mock_def.return_value = (b"""
         TEXT:
             ***
                NOT VALID