We can constant-fold JSLoadProperty(o, i) when o is a known object (i.e.
TurboFan's context specialization provides a known non-null/-undefined
constant value for it), i is a known array index and o["i"] is an
element on the receiver, that is non-configurable and non-writable (i.e.
o was frozen using Object.freeze earlier, or o is a String object).

This significantly reduces execution time of the tagged templates
micro-benchmarks (ES6 and Babel transpiled), when combined with the
CL https://chromium-review.googlesource.com/c/v8/v8/+/677462, it goes
from

  templateStringTagES5: 4552 ms.
  templateStringTagES6: 14185 ms.
  templateStringTagBabel: 7626 ms.

to

  templateStringTagES5: 4550 ms.
  templateStringTagES6: 616 ms.
  templateStringTagBabel: 589 ms.

so overall a solid 23x improvement on the ES6 benchmark. This is
representative of the six-speed-templatestringtag-es6 benchmark.

Bug: v8:6819, v8:6820, v8:6831
Change-Id: Ia45fbdf92977bfbe7400cfa60bd362b78086dc26
Reviewed-on: https://chromium-review.googlesource.com/677603Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48131}