message: [language/vm-runtime] make Interpreter private to the crate
  This isn't used anywhere, nor should it be.
  Closes:
  Approved by: dariorussi
diff: @@ -110,7 +110,7 @@ fn derive_type_tag(
  // REVIEW: abstract the data store better (maybe a single Trait for both data and event?)
  // The ModuleCache should be a Loader with a proper API.
  // Resolve where GasMeter should live.
  -pub struct Interpreter<'txn> {
  +pub(crate) struct Interpreter<'txn> {
  /// Operand stack, where Move `Value`s are stored for stack operations.
  operand_stack: Stack,
  /// The stack of active functions.
  