- New invariant on union types: if the union has a range then the number
  bits in the bitset must be cleared.

- Various tweaks in intersection and union to satisfy the invariant.

- Exposed and used representation bits in range types (and the Limits
  helper class).

- Implemented Glb for ranges so that the Is predicate handles
  ranges correctly.

- Change typer weakening so that it does not rely on GetRange.
  However, the code still seems to be a bit fragile.

- Removed the Smi types from the type system core, instead introduced
  Signed31, Unsigned30 and created constructors for Small(Un)Signed
  that point to the right type for the architecture.

- Punched a hole in the config to be able to get to the isolate so
  that it is possible to allocate heap numbers for newly created
  ranges.

Patch by jarin@chromium.prg, original review here:
https://codereview.chromium.org/795713003/

TBR=jarin@chromium.org
BUG=

Review URL: https://codereview.chromium.org/837723006

Cr-Commit-Position: refs/heads/master@{#26197}