This adds an "experimental" API hook (v8::ScriptCompiler::CompileModule)
allowing compilation of modules. The code gen is incredibly basic: the
module body is represented by a Block in the AST. But this at least gets
more of the pipeline working, and opens the door to writing mjsunit tests
(once d8 is modified to support module compilation).

BUG=v8:1569
LOG=n

Review URL: https://codereview.chromium.org/902093002

Cr-Commit-Position: refs/heads/master@{#26496}