Refactor git.Command.Run*, introduce RunWithContextString and RunWithContextBytes (#19266)

This follows 
* https://github.com/go-gitea/gitea/issues/18553

Introduce `RunWithContextString` and `RunWithContextBytes` to help the refactoring. Add related unit tests. They keep the same behavior to save stderr into err.Error() as `RunInXxx` before.

Remove `RunInDirTimeoutPipeline` `RunInDirTimeoutFullPipeline` `RunInDirTimeout` `RunInDirTimeoutEnv`  `RunInDirPipeline`  `RunInDirFullPipeline`  `RunTimeout`, `RunInDirTimeoutEnvPipeline`, `RunInDirTimeoutEnvFullPipeline`, `RunInDirTimeoutEnvFullPipelineFunc`.

Then remaining `RunInDir` `RunInDirBytes` `RunInDirWithEnv` can be easily refactored in next PR with a simple search & replace:
* before: `stdout, err := RunInDir(path)`
* next: `stdout, _, err := RunWithContextString(&git.RunContext{Dir:path})`

Other changes:
1. When `timeout <= 0`, use default. Because `timeout==0` is meaningless and could cause bugs. And now many functions becomes more simple, eg: `GitGcRepos` 9 lines to 1 line. `Fsck` 6 lines to 1 line.
2. Only set defaultCommandExecutionTimeout when the option `setting.Git.Timeout.Default > 0`

modules/git/command_race_test.go

@@ -0,0 +1,40 @@
+// Copyright 2017 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+//go:build race
+// +build race
+
+package git
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestRunWithContextNoTimeout(t *testing.T) {
+	maxLoops := 10
+
+	// 'git --version' does not block so it must be finished before the timeout triggered.
+	cmd := NewCommand(context.Background(), "--version")
+	for i := 0; i < maxLoops; i++ {
+		if err := cmd.RunWithContext(&RunContext{}); err != nil {
+			t.Fatal(err)
+		}
+	}
+}
+
+func TestRunWithContextTimeout(t *testing.T) {
+	maxLoops := 10
+
+	// 'git hash-object --stdin' blocks on stdin so we can have the timeout triggered.
+	cmd := NewCommand(context.Background(), "hash-object", "--stdin")
+	for i := 0; i < maxLoops; i++ {
+		if err := cmd.RunWithContext(&RunContext{Timeout: 1 * time.Millisecond}); err != nil {
+			if err != context.DeadlineExceeded {
+				t.Fatalf("Testing %d/%d: %v", i, maxLoops, err)
+			}
+		}
+	}
+}