Replaced access path bases with access paths in backward dataflow

[MForest7]

Replaced nested objects in backward dataflow with access paths, also get a performance increase.

project	stmts	avg time (main)	avg time (new)	aa improvement, % (old)	aa improvement, % (new)
project1	9914	2.5s	1.6s	37.2	39.4
project2	26679	2.2s	1.4s	15.3	16.5
project3	4272	0.8s	0.4s	29.0	28.8
project4	4584	0.5s	0.3s	37.5	35.6
project5	121091	30.4s	9.3s	35.3	37.4
project6	28548	3.3s	1.7s	36.8	38.9
project7	5162	0.6s	0.4s	28.1	28.0

[Lipen]

For the future reference: this PR disrupted the "saved types" trick for handling new T with unresolved T, in particular, the filling of typeInfo (later passed to savedTypes in Forward FF) in Backward FF was removed since it is either can't be expressed anymore, or it is just not clear how to do it straight. Consequently, I have removed the whole "saved types" logic from Forward FF to clean-up the code.

Below is the failing test with unresolved T and "expected" type which could be passed only with saved types trick, but it is not clean whether we even need to support such case. So, we have decided to currently disable such test.

class CaseNew2 {
    entrypoint() {
        let x = new Something(); // unresolved
        let y = x.foo; // use 'foo' field
        this.infer(x);
    }
    infer(a: any): any {
        const EXPECTED_ARG_0 = "Something { foo: any }";
    }
}