generate-bytecode-expectations is a tool intended to work together
with test/cctest/test-bytecode-generator.cc in order to produce a
meaningful diff between testcases and the actual bytecode being emitted.

It does so by parsing and compiling Javascript to bytecode,
constructing the same data structure in the testcase and then running a
textual diff between the expected (i.e. the one encoded in the unit test)
and actual (i.e. the one built from the compiler output) representation.

This commit is a first step in this direction, achieving just the first
half of what we desire. At the moment, bytecodechecker can:

* take a code snippet from the command line and emit the expected structure.
* adhere to the same formatting rules of the test cases
  (this one is important for text diff and for copy and pasting too)

Still to do:

* parse unit tests:
    + extract code snippets
    + indent the code to match the input test case
    + allow flexibility in the input format
    + try to recognize and work around some macro magic (i.e. REPEAT_127)
* emit the representation of the constant pool and handlers vector
* run a textual diff

BUG=v8:4280
LOG=N

Review URL: https://codereview.chromium.org/1671863002

Cr-Commit-Position: refs/heads/master@{#33863}