Fix mangling of --json output of utf-8 characters when not running in a utf-8 locale

As long as all code imports Utility.Aeson rather than Data.Aeson,
and no Strings that may contain utf-8 characters are used for eg, object
keys via T.pack, this is guaranteed to fix the problem everywhere that
git-annex generates json.

It's kind of annoying to need to wrap ToJSON with a ToJSON', especially
since every data type that has a ToJSON instance has to be ported over.
However, that only took 50 lines of code, which is worth it to ensure full
coverage. I initially tried an alternative approach of a newtype FileEncoded,
which had to be used everywhere a String was fed into aeson, and chasing
down all the sites would have been far too hard. Did consider creating an
intentionally overlapping instance ToJSON String, and letting ghc fail
to build anything that passed in a String, but am not sure that wouldn't
pollute some library that git-annex depends on that happens to use ToJSON
String internally.

This commit was supported by the NSF-funded DataLad project.

Test.hs

@@ -21,7 +21,6 @@ import Test.Tasty.Ingredients.Rerun
 import Options.Applicative (switch, long, help, internal)
 
 import qualified Data.Map as M
-import qualified Data.Aeson
 import qualified Data.ByteString.Lazy.UTF8 as BU8
 import System.Environment
 
@@ -83,6 +82,7 @@ import qualified Utility.HumanTime
 import qualified Utility.Base64
 import qualified Utility.Tmp.Dir
 import qualified Utility.FileSystemEncoding
+import qualified Utility.Aeson
 #ifndef mingw32_HOST_OS
 import qualified Remote.Helper.Encryptable
 import qualified Types.Crypto
@@ -971,7 +971,7 @@ test_merge = intmpclonerepo $
 test_info :: Assertion
 test_info = intmpclonerepo $ do
 	json <- BU8.fromString <$> git_annex_output "info" ["--json"]
-	case Data.Aeson.eitherDecode json :: Either String Data.Aeson.Value of
+	case Utility.Aeson.eitherDecode json :: Either String Utility.Aeson.Value of
 		Right _ -> return ()
 		Left e -> assertFailure e