add System.FilePath to this conversion

It seems to make sense to convert both System.Directory and
System.FilePath uses to OsPath in one go. This will generally look like
replacing RawFilePath with OsPath in type signatures, and will be driven
by the now absolutely massive pile of compile errors.

Got a few modules building in this new regime.

Sponsored-by: Jack Hill

Utility/OsPath.hs

@@ -13,17 +13,24 @@
 module Utility.OsPath (
 	OsPath,
 	OsString,
+	RawFilePath,
 	literalOsPath,
 	toOsPath,
 	fromOsPath,
+	module X,
+	getSearchPath,
 ) where
 
 import Utility.FileSystemEncoding
 #ifdef WITH_OSPATH
+import System.OsPath as X hiding (OsPath, OsString)
 import System.OsPath
 import "os-string" System.OsString.Internal.Types
 import qualified Data.ByteString.Short as S
+import qualified System.FilePath.ByteString as PB
 #else
+import System.FilePath.ByteString as X hiding (RawFilePath, getSearchPath)
+import System.FilePath.ByteString (getSearchPath)
 import qualified Data.ByteString as S
 #endif
 
@@ -61,6 +68,10 @@ bytesFromOsPath = S.fromShort . getWindowsString . getOsString
 bytesFromOsPath = S.fromShort . getPosixString . getOsString
 #endif
 
+{- For some reason not included in System.OsPath -}
+getSearchPath :: IO [OsPath]
+getSearchPath = map toOsPath <$> PB.getSearchPath
+
 #else
 {- When not building with WITH_OSPATH, use RawFilePath.
  -}