This introduces optimized number operations based on type feedback.

Summary of changes:

1. Typed lowering produces SpeculativeNumberAdd/Subtract for JSAdd/Subtract if
   there is suitable feedback. The speculative nodes are connected to both the
   effect chain and the control chain and they retain the eager frame state.

2. Simplified lowering now executes in three phases:
  a. Propagation phase computes truncations by traversing the graph from uses to
     definitions until checkpoint is reached. It also records type-check decisions
     for later typing phase, and computes representation.
  b. The typing phase computes more precise types base on the speculative types (and recomputes
     representation for affected nodes).
  c. The lowering phase performs lowering and inserts representation changes and/or checks.

3. Effect-control linearization lowers the checks to machine graphs.

Notes:

- SimplifiedLowering will be refactored to have handling of each operation one place and
  with clearer input/output protocol for each sub-phase. I would prefer to do this once
  we have more operations implemented, and the pattern is clearer.

- The check operations (Checked<A>To<B>) should have some flags that would affect
  the kind of truncations that they can handle. E.g., if we know that a node produces
  a number, we can omit the oddball check in the CheckedTaggedToFloat64 lowering.

- In future, we want the typer to reuse the logic from OperationTyper.

BUG=v8:4583
LOG=n

Review-Url: https://codereview.chromium.org/1921563002
Cr-Commit-Position: refs/heads/master@{#36674}