DebugInfo was very closely tied to break point support:
* It contained only information relevant to break points.
* It was created and freed by break point implementation.
* Existence of a DebugInfo on the shared function info implied existence of
  break points.

This CL is a step towards making DebugInfo usable by other debugging
functionality such as block coverage by decoupling it from break point support,
which is now only one kind of information stored on the DebugInfo object.

BUG=v8:6000

Review-Url: https://codereview.chromium.org/2909893002
Cr-Commit-Position: refs/heads/master@{#45640}