Always evaluate on [[GetOwnProperty]] of a string

[nicolo-ribaudo]

Since #33, the [[Get]] internal method of namespace objects was updated to do:

• if the property key is a symbol, do an ordinary get and return.
• if the namespace is deferred, evaluate it
• if the property key is not a known export, return undefined
• get the export value and return it

I was assuming that [[GetOwnProperty]] would do the same, since it internally uses [[Get]]. However, what it did was:

• if the property key is a symbol, do an ordinary getOwnProperty and return.
• if the property key is not a known export, return undefined
• call [[Get]]
• return a property descriptor

Which means that, even if it calls [[Get]], its effect is still gated on the existence of the property. For consistency, this PR triggers evaluation in [[GetOwnProperty]] before checking whether the property is a known export or not.

[Jack-Works]

can we only evaluate iff the key is an export name? I don't want to see things like if(mod.__esModule) let the optimization fails

[nicolo-ribaudo]

@Jack-Works I'm going to present that as an option. Although, mod.__esModule is checked in transpiled code and thus tools can special-case it.