Similar to Value::to_string_without_side_effects() this is mostly a
regular object property lookup, but with the guarantee that it will be
side-effect free, i.e. no accessors or native property functions will
be called. This is needed when we want to access user-controlled object
properties for debug logging, for example. The specific use case will be
error objects which will soon no longer have internal name/message
properties, so we need to guarantee that printing an error, which may
already be the result of an exception, won't blow up in our face :^)
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