code_review: PR #1055

- since the author and time are already shown in the blame view, use the full message as tooltip is better.
- cache the commit message in `ViewModels.Blame` since the `Tooltip` of control may change.
- querying commit message synchronously (it's very fast) to avoid similar issues in commit details panel.

Signed-off-by: leo <longshuang@msn.cn>

src/ViewModels/Blame.cs

@@ -1,4 +1,5 @@
-using System.Threading.Tasks;
+using System.Collections.Generic;
+using System.Threading.Tasks;
 
 using Avalonia.Threading;
 
@@ -57,12 +58,18 @@ namespace SourceGit.ViewModels
             }
         }
 
-        public Models.Commit GetCommitInfo(string commitSHA)
+        public string GetCommitMessage(string sha)
         {
-            return new Commands.QuerySingleCommit(_repo, commitSHA).Result();
+            if (_commitMessages.TryGetValue(sha, out var msg))
+                return msg;
+
+            msg = new Commands.QueryCommitFullMessage(_repo, sha).Result();
+            _commitMessages[sha] = msg;
+            return msg;
         }
 
         private readonly string _repo;
         private Models.BlameData _data = null;
+        private Dictionary<string, string> _commitMessages = new Dictionary<string, string>();
     }
 }