Refactor "change file" API (#34855)

Follow up the "editor" refactor, use the same approach to simplify code,
and fix some docs & comments

---------

Signed-off-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>

tests/integration/api_repo_file_delete_test.go

@@ -20,20 +20,22 @@ import (
 
 func getDeleteFileOptions() *api.DeleteFileOptions {
 	return &api.DeleteFileOptions{
-		FileOptions: api.FileOptions{
-			BranchName:    "master",
-			NewBranchName: "master",
-			Message:       "Removing the file new/file.txt",
-			Author: api.Identity{
-				Name:  "John Doe",
-				Email: "johndoe@example.com",
-			},
-			Committer: api.Identity{
-				Name:  "Jane Doe",
-				Email: "janedoe@example.com",
+		FileOptionsWithSHA: api.FileOptionsWithSHA{
+			FileOptions: api.FileOptions{
+				BranchName:    "master",
+				NewBranchName: "master",
+				Message:       "Removing the file new/file.txt",
+				Author: api.Identity{
+					Name:  "John Doe",
+					Email: "johndoe@example.com",
+				},
+				Committer: api.Identity{
+					Name:  "Jane Doe",
+					Email: "janedoe@example.com",
+				},
 			},
+			SHA: "103ff9234cefeee5ec5361d22b49fbb04d385885",
 		},
-		SHA: "103ff9234cefeee5ec5361d22b49fbb04d385885",
 	}
 }
 
@@ -110,7 +112,7 @@ func TestAPIDeleteFile(t *testing.T) {
 		deleteFileOptions.SHA = "badsha"
 		req = NewRequestWithJSON(t, "DELETE", fmt.Sprintf("/api/v1/repos/%s/%s/contents/%s", user2.Name, repo1.Name, treePath), &deleteFileOptions).
 			AddTokenAuth(token2)
-		MakeRequest(t, req, http.StatusBadRequest)
+		MakeRequest(t, req, http.StatusUnprocessableEntity)
 
 		// Test creating a file in repo16 by user4 who does not have write access
 		fileID++