adjust unlocked execute bit handling

When building an adjusted unlocked branch, make pointer files executable
when the annex object file is executable.

This slows down git-annex adjust --unlock/--unlock-present by needing to
stat all annex object files in the tree. Probably not a significant
slowdown compared to other work they do, but I have not benchmarked.

I chose to leave git-annex adjust --unlock marked as stable, even though
get or drop of an object file can change whether it would make the pointer
file executable. Partly because making it unstable would slow down
re-adjustment, and partly for symmetry with the handling of an unlocked
pointer file that is executable when the content is dropped, which does not
remove its execute bit.

Annex/AdjustedBranch.hs

@@ -1,6 +1,6 @@
 {- adjusted branch
  -
- - Copyright 2016-2023 Joey Hess <id@joeyh.name>
+ - Copyright 2016-2024 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -68,9 +68,12 @@ import qualified Database.Keys
 import Config
 import Logs.View (is_branchView)
 import Logs.AdjustedBranchUpdate
+import Utility.FileMode
+import qualified Utility.RawFilePath as R
 
 import Data.Time.Clock.POSIX
 import qualified Data.Map as M
+import System.PosixCompat.Files (fileMode)
 
 class AdjustTreeItem t where
 	-- How to perform various adjustments to a TreeItem.
@@ -155,8 +158,13 @@ adjustToPointer :: TreeItem -> Annex (Maybe TreeItem)
 adjustToPointer ti@(TreeItem f _m s) = catKey s >>= \case
 	Just k -> do
 		Database.Keys.addAssociatedFile k f
-		Just . TreeItem f (fromTreeItemType TreeFile)
-			<$> hashPointerFile k
+		exe <- catchDefaultIO False $
+			(isExecutable . fileMode) <$> 
+				(liftIO . R.getFileStatus
+					=<< calcRepo (gitAnnexLocation k))
+		let mode = fromTreeItemType $ 
+			if exe then TreeExecutable else TreeFile
+		Just . TreeItem f mode <$> hashPointerFile k
 	Nothing -> return (Just ti)
 
 adjustToSymlink :: TreeItem -> Annex (Maybe TreeItem)