[rust-compiler] Fix identifierName in validation diagnostics and error formatting

- Add identifier_name extraction in validate_no_derived_computations_in_effects
  and validate_no_set_state_in_effects using source code byte offsets
- Add identifier_name_for_id helper to Environment
- Fix BabelPlugin error formatting: scope extraction errors, raw exception messages
- Add raw_message field to CompilerErrorInfo for unknown exception passthrough

Snap: 1644→1661/1718 (+17).