RevisionReader: Parse raw commit body

* Parse raw body %B instead of combining %s%n%n%b to avoid extra processing
in both Git and GE.
Simplify the handling.

* Do not allocate body for older commits
Previously a temporary variable was allocated also if body was
not stored in the commit message (to save memory, for older commits).

* Only store commit body if multiline message
If the body is the same as the subject, do not store the message
This also avoids loading the commit body for older commits
if the commit is selected

* Align usage of commit body retrieval for other than RevisionReader
  * "Previous commit messages" used %s%b instead of %B
  * Align parsing of raw body and subject

* ObjectId Inline local parsing functions

* Use ReadOnlySpan<char> in RevisionReader
Reduce string allocations

* Use HighPerformance StringBuffer

GitCommands/Git/GitModule.cs

@@ -950,11 +950,18 @@ public GitRevision GetRevision(ObjectId? objectId = null, bool shortFormat = fal
             }
             else
             {
-                string message = ProcessDiffNotes(10);
+                string message = ProcessDiffNotes(startIndex: 10);
 
                 // commit message is not re-encoded by git when format is given
-                revision.Body = ReEncodeCommitMessage(message, revision.MessageEncoding);
-                revision.Subject = revision.Body?.Substring(0, revision.Body.IndexOfAny(new[] { '\r', '\n' })) ?? "";
+                // See also RevisionReader for parsing commit body
+                string body = ReEncodeCommitMessage(message, revision.MessageEncoding);
+                revision.Body = body;
+
+                ReadOnlySpan<char> span = (body ?? "").AsSpan();
+                int endSubjectIndex = span.IndexOf('\n');
+                revision.Subject = endSubjectIndex >= 0
+                    ? span.Slice(0, endSubjectIndex).TrimEnd().ToString()
+                    : body ?? "";
             }
 
             if (loadRefs)
@@ -3507,7 +3514,7 @@ public string GetFileText(ObjectId id, Encoding encoding)
                 "-z",
                 $"-n {count}",
                 revision,
-                "--pretty=format:%e%n%s%n%n%b",
+                "--pretty=format:%e%n%B",
                 { !string.IsNullOrEmpty(authorPattern), string.Concat("--author=\"", authorPattern, "\"") }
             };
 
@@ -3884,7 +3891,7 @@ public bool IsRunningGitProcess()
         // there was a bug: Git before v1.8.4 did not recode commit message when format is given
         // Lossless encoding is used, because LogOutputEncoding might not be lossless and not recoded
         // characters could be replaced by replacement character while re-encoding to LogOutputEncoding
-        public string ReEncodeCommitMessage(string s, string? toEncodingName)
+        public string? ReEncodeCommitMessage(string s, string? toEncodingName)
         {
             Encoding? encoding;
             try
@@ -3896,7 +3903,7 @@ public string ReEncodeCommitMessage(string s, string? toEncodingName)
                 return s + "\n\n! Unsupported commit message encoding: " + toEncodingName + " !";
             }
 
-            return ReEncodeStringFromLossless(s, encoding);
+            return ReEncodeStringFromLossless(s, encoding)?.Trim();
         }
 
         public Encoding? GetEncodingByGitName(string? encodingName)

GitCommands/GitCommands.csproj

@@ -22,6 +22,7 @@
 
   <ItemGroup>
     <PackageReference Include="JetBrains.Annotations" />
+    <PackageReference Include="Microsoft.Toolkit.HighPerformance" />
     <PackageReference Include="Newtonsoft.Json" />
     <PackageReference Include="System.IO.Abstractions" />
     <PackageReference Include="System.Reactive.Linq" />