cmd/syncthing: Add decrypt subcommand (#7332)

This adds the `syncthing decrypt` subcommand that is used to
(offline-)decrypt or just verify the contents of an encrypted folder.

lib/config/folderconfiguration.go

@@ -29,6 +29,7 @@ var (
 
 const (
 	DefaultMarkerName          = ".stfolder"
+	EncryptionTokenName        = "syncthing-encryption_password_token"
 	maxConcurrentWritesDefault = 2
 	maxConcurrentWritesLimit   = 64
 )

lib/model/model.go

@@ -3135,7 +3135,7 @@ func (s deviceIDSet) AsSlice() []protocol.DeviceID {
 }
 
 func encryptionTokenPath(cfg config.FolderConfiguration) string {
-	return filepath.Join(cfg.MarkerName, "syncthing-encryption_password_token")
+	return filepath.Join(cfg.MarkerName, config.EncryptionTokenName)
 }
 
 type storedEncryptionToken struct {