Errors that reach checked-dynamic code are objects carrying the reserved
"%error" marker, with name and message either own or on their prototype.
Several string conversions handled them differently from Node:
- `"" + error`, `error + ""` and `error == "TypeError: ..."` converted
through the plain-object path and answered "[object Object]".
- Template literals and Array join read name and message as own members
only, so a builtin error whose name is inherited printed its message
alone.
- String(error) used the native error, which did not see name and message
assigned through the dynamic view.
scr_dyn_error_string implements Error.prototype.toString over the
encoding, reading both members through the prototype, and the template
renderer, Array join, ToPrimitive, ToString and the numeric conversion use
it. Assigning a string name or message through the dynamic view now also
updates the native error, as assigning stack and cause already did.
