Backport of Handle `-help` usage in stacks plugin into v1.14 (#37655)

* backport of commit 10f00d437f

* backport of commit 7f0ef4c8d0

---------

Co-authored-by: Mark DeCrane <mark.decrane@hashicorp.com>

.changes/v1.14/ENHANCEMENTS-20250919-115253.yaml

@@ -0,0 +1,5 @@
+kind: ENHANCEMENTS
+body: '`terraform stacks` command support for `-help` flag'
+time: 2025-09-19T11:52:53.923764-04:00
+custom:
+    Issue: "37645"

internal/command/stacks.go

@@ -82,7 +82,6 @@ func (c *StacksCommand) realRun(args []string, stdout, stderr io.Writer) int {
 	args = c.Meta.process(args)
 	cmdFlags := c.Meta.defaultFlagSet("stacks")
 	cmdFlags.StringVar(&pluginCacheDirOverride, "plugin-cache-dir", "", "plugin cache directory")
-	cmdFlags.Usage = func() { c.Ui.Error(c.Help()) }
 	cmdFlags.Parse(args)
 
 	if pluginCacheDirOverride != "" {
@@ -379,8 +378,17 @@ func (c *StacksCommand) Run(args []string) int {
 // Help returns help text for the stacks command.
 func (c *StacksCommand) Help() string {
 	helpText := new(bytes.Buffer)
-	if exitCode := c.realRun([]string{}, helpText, io.Discard); exitCode != 0 {
-		return ""
+	errorText := new(bytes.Buffer)
+
+	parsedArgs := []string{}
+	for _, arg := range os.Args[1:] {
+		if arg == "stacks" {
+			continue // skip stacks command name
+		}
+		parsedArgs = append(parsedArgs, arg)
+	}
+	if exitCode := c.realRun(parsedArgs, helpText, errorText); exitCode != 0 {
+		return errorText.String()
 	}
 
 	return helpText.String()