Refactor plugin catalog and plugin runtime catalog into their own package (#24403)

* Refactor plugin catalog into its own package
* Fix some unnecessarily slow tests due to accidentally running multiple plugin processes
* Clean up MakeTestPluginDir helper
* Move getBackendVersion tests to plugin catalog package
* Use corehelpers.MakeTestPlugin consistently
* Fix semgrep failure: check for nil value from logical.Storage

helper/testhelpers/corehelpers/corehelpers.go

@@ -49,36 +49,27 @@ func RetryUntil(t testing.T, timeout time.Duration, f func() error) {
 
 // MakeTestPluginDir creates a temporary directory suitable for holding plugins.
 // This helper also resolves symlinks to make tests happy on OS X.
-func MakeTestPluginDir(t testing.T) (string, func(t testing.T)) {
-	if t != nil {
-		t.Helper()
-	}
+func MakeTestPluginDir(t testing.T) string {
+	t.Helper()
 
 	dir, err := os.MkdirTemp("", "")
 	if err != nil {
-		if t == nil {
-			panic(err)
-		}
 		t.Fatal(err)
 	}
 
 	// OSX tempdir are /var, but actually symlinked to /private/var
 	dir, err = filepath.EvalSymlinks(dir)
 	if err != nil {
-		if t == nil {
-			panic(err)
-		}
 		t.Fatal(err)
 	}
 
-	return dir, func(t testing.T) {
+	t.Cleanup(func() {
 		if err := os.RemoveAll(dir); err != nil {
-			if t == nil {
-				panic(err)
-			}
 			t.Fatal(err)
 		}
-	}
+	})
+
+	return dir
 }
 
 func NewMockBuiltinRegistry() *mockBuiltinRegistry {