This implements graph construction for entry via on-stack replacement
within the {BytecodeGraphBuilder}. Entry points are at loop headers
similar to previous OSR implementations. All interpreter registers are
addressable via {OsrValue} nodes in the graph. Currently we rely on
{OsrPoll} bytecodes to be placed right after loop headers (i.e. at the
targets of back edges).

R=jarin@chromium.org
BUG=v8:4764

Review-Url: https://codereview.chromium.org/2171083004
Cr-Commit-Position: refs/heads/master@{#38083}