This is a CL in a string of CLs that template SimplifiedLowering.
It is done with the purpose of decoupling the implementation in the
three phases that SimplifiedLowering has (Propagate, Retype, Lower).

Template lower(), retype() and propagate(). Remove phase_ since it is
not needed anymore.

Template methods that used the old version of lower() and similar:
 * EnqueueInput
 * SetOutput
 * ProcessInput
 * VisitLeaf
 * VisitSelect
 * VisitPhi
 * VisitStateValues
 * VisitFrameState
 * VisitObjectState

Bug: v8:10424
Change-Id: Ic7c22104a77892303d825ad2d75e0eda56cca754
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2135638
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67402}