RevisionDiff: Stage/Unstage selected lines

Move handling of stage/unstage/reset line patching from FormCommit to FileViewer.
Instead of FormCommit adding menu items to FileViewer, handle
the actions directly in FileViewer, including the hotkey handling.
Also hotkey for cherry-pick and reset line patches.
This also aligns the stage/reset menu items to other forms.

Apply the line patching also to RevDiff, supporting line patches for
worktree/index properly, including hotkey handling.
When manipulating a diff with an artificial commit, refresh the diff
after patching.

Some code cleanup, like using ViewChangesAsync consistently for diffs/patches

FormCommit; Use common method for head revisions
Set parents for artificial revisions

GitCommands/Git/GitModule.cs

@@ -2449,7 +2449,7 @@ public IReadOnlyList<GitItemStatus> GetDiffFilesWithSubmodulesStatus(ObjectId fi
         /// <param name="secondId">to revision</param>
         /// <param name="parentToSecond">The parent for the second revision</param>
         /// <remarks>Git revisions are required to determine if <see cref="StagedStatus"/> allows stage/unstage.</remarks>
-        private static StagedStatus GetStagedStatus([CanBeNull] ObjectId firstId, [CanBeNull] ObjectId secondId, [CanBeNull] ObjectId parentToSecond)
+        public static StagedStatus GetStagedStatus([CanBeNull] ObjectId firstId, [CanBeNull] ObjectId secondId, [CanBeNull] ObjectId parentToSecond)
         {
             StagedStatus staged;
             if (firstId == ObjectId.IndexId && secondId == ObjectId.WorkTreeId)

GitUI/CommandsDialogs/RevisionDiffControl.cs

@@ -59,6 +59,7 @@ public RevisionDiffControl()
             _revisionDiffContextMenuController = new FileStatusListContextMenuController();
             DiffText.TopScrollReached += FileViewer_TopScrollReached;
             DiffText.BottomScrollReached += FileViewer_BottomScrollReached;
+            DiffText.LinePatchingBlocksUntilReload = true;
         }
 
         private void FileViewer_TopScrollReached(object sender, EventArgs e)
@@ -335,7 +336,7 @@ private ContextMenuSelectionInfo GetSelectionInfo()
             bool isAnyTracked = selectedItems.Any(item => item.Item.IsTracked);
             bool isAnyIndex = selectedItems.Any(item => item.Item.Staged == StagedStatus.Index);
             bool isAnyWorkTree = selectedItems.Any(item => item.Item.Staged == StagedStatus.WorkTree);
-            bool supportPatches = selectedGitItemCount == 1 && DiffText.HasAnyPatches();
+            bool supportPatches = selectedGitItemCount == 1 && DiffText.SupportLinePatching;
             bool isDeleted = selectedItems.Any(item => item.Item.IsDeleted);
             bool isAnySubmodule = selectedItems.Any(item => item.Item.IsSubmodule);
             (bool allFilesExist, bool allDirectoriesExist, bool allFilesOrUntrackedDirectoriesExist) = FileOrUntrackedDirExists(selectedItems, _fullPathResolver);
@@ -479,6 +480,11 @@ private void DiffText_ExtraDiffArgumentsChanged(object sender, EventArgs e)
             }).FileAndForget();
         }
 
+        private void DiffText_PatchApplied(object sender, EventArgs e)
+        {
+            RefreshArtificial();
+        }
+
         private void diffShowInFileTreeToolStripMenuItem_Click(object sender, EventArgs e)
         {
             // switch to view (and fills the first level of file tree data model if not already done)

GitUI/CommandsDialogs/RevisionDiffController.cs

@@ -117,6 +117,7 @@ public bool ShouldShowMenuCherryPick(ContextMenuSelectionInfo selectionInfo)
                 && !selectionInfo.IsBareRepository
                 && selectionInfo.AllFilesExist
                 && selectionInfo.SupportPatches
+                && !(selectionInfo.IsAnyItemWorkTree || selectionInfo.IsAnyItemIndex)
                 && !(selectionInfo.SelectedRevision?.IsArtificial ?? false);
         }