Adds basic support for generation of interpreter bytecode handler code
snippets. The InterpreterAssembler class exposes a set of low level,
interpreter specific operations which can be used to build a Turbofan
graph. The Interpreter class generates a bytecode handler snippet for
each bytecode by assembling operations using an InterpreterAssembler.

Currently only two simple bytecodes are supported: LoadLiteral0 and Return.

BUG=v8:4280
LOG=N

Review URL: https://codereview.chromium.org/1239793002

Cr-Commit-Position: refs/heads/master@{#29814}