This adds the --ignition-preserve-bytecode flag which will preserve any
existing bytecode, even if a tier-up to baseline code is performed. This
is preparatory work in order to allow mixed stacks where bytecode and
baseline code can be active at the same time.

It also adds a {HasBaselineCode} predicate symmetric to the existing
{HasBytecodeArray} predicate. Both predicates are independent and any
combination of answers is valid.

Further adaptation of the rest of the runtime will be done step-wise in
follow-up changes.

R=yangguo@chromium.org
BUG=v8:5265

Review-Url: https://codereview.chromium.org/2224923003
Cr-Commit-Position: refs/heads/master@{#38540}