Don't replace missing object members with undefined

[mischnic]

In general, {}.foo shouldn't be replaced with undefined because

1. the properties on the object prototype aren't undefined ({}.constructor itself, {}.hasOwnProperty, ...) and
2. hypothetically, the object's prototype could have been modified: ({}.__proto__).foo = 2; console.log({}.foo)

Instead, only member accesses for properties that actually exists should be replaced

The fix seems to work, but I'm not so sure about the added test: reverting the change to the simplifier, this is the test output:

---- simplify::branch::tests::test_object_literal stdout ----
----- Actual -----
----- Actual -----
----- Actual -----
----- Actual -----
----- Actual -----
>>>>> Orig <<<<<
({}).foo
>>>>> Code <<<<<

thread 'simplify::branch::tests::test_object_literal' panicked at 'assertion failed: `(left == right)`
            ({
}).foo;

shouldn't it say something like Expected: '({}).foo', Actual: 'undefined'?

[CLAassistant]

All committers have signed the CLA.

[kdy1]

LGTM. Thanks!