Fix PropertyHook::getStmts() for set hook

Produce the correct desugaring if the propertyName attribute is
set, and set it in the parser. Otherwise throw an exception.

Fixes #105

Fix PropertyHook::getStmts() for set hook

Produce the correct desugaring if the propertyName attribute is
set, and set it in the parser. Otherwise throw an exception.

Fixes #1053.

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Fix cs

Make PropertyHook::getStmts() less incorrect

Still missing the assignment to the correct property, but at
least we're not returning from a non-void function now...

Add `PropertyHook::isFinal()` helper method with tests