don't stringify hash keys in Base#initialize

[notEthan]

while it may arguably be better for a JSI to treat hash keys that are symbols as if they were strings, calling deep_stringify_symbol_keys in Base#initialize is, for one thing, very much a half-assed solution since some_jsi[:foo] is not the same as some_jsi['foo'], and also problematic in that the JSI's instance then may or may not refer to the same actual object as the instance that was passed to #initialize.

in the future I might decide that Base#initialize does a deep stringifying copy of its instance if I fully implement something more like ActiveSupport::HashWithIndifferentAccess within JSI::Base. but I kind of doubt it.