Refactor git command stdio pipe (#36422)

Most potential deadlock problems should have been fixed, and new code is
unlikely to cause new problems with the new design.

Also raise the minimum Git version required to 2.6.0 (released in 2015)

routers/web/repo/githttp.go

@@ -446,8 +446,8 @@ func serviceRPC(ctx *context.Context, service string) {
 
 	if err := gitrepo.RunCmdWithStderr(ctx, h.getStorageRepo(), cmd.AddArguments(".").
 		WithEnv(append(os.Environ(), h.environ...)).
-		WithStdin(reqBody).
-		WithStdout(ctx.Resp),
+		WithStdinCopy(reqBody).
+		WithStdoutCopy(ctx.Resp),
 	); err != nil {
 		if !gitcmd.IsErrorCanceledOrKilled(err) {
 			log.Error("Fail to serve RPC(%s) in %s: %v", service, h.getStorageRepo().RelativePath(), err)

routers/web/repo/setting/lfs.go

@@ -407,7 +407,9 @@ func LFSPointerFiles(ctx *context.Context) {
 	err = func() error {
 		pointerChan := make(chan lfs.PointerBlob)
 		errChan := make(chan error, 1)
-		go lfs.SearchPointerBlobs(ctx, ctx.Repo.GitRepo, pointerChan, errChan)
+		go func() {
+			errChan <- lfs.SearchPointerBlobs(ctx, ctx.Repo.GitRepo, pointerChan)
+		}()
 
 		numPointers := 0
 		var numAssociated, numNoExist, numAssociatable int
@@ -483,11 +485,6 @@ func LFSPointerFiles(ctx *context.Context) {
 			results = append(results, result)
 		}
 
-		err, has := <-errChan
-		if has {
-			return err
-		}
-
 		ctx.Data["Pointers"] = results
 		ctx.Data["NumPointers"] = numPointers
 		ctx.Data["NumAssociated"] = numAssociated
@@ -495,7 +492,8 @@ func LFSPointerFiles(ctx *context.Context) {
 		ctx.Data["NumNoExist"] = numNoExist
 		ctx.Data["NumNotAssociated"] = numPointers - numAssociated
 
-		return nil
+		err := <-errChan
+		return err
 	}()
 	if err != nil {
 		ctx.ServerError("LFSPointerFiles", err)