Extract script formatter worker in a separate build target

Files that used by ScriptFormatterWorker exclusively were removed from devtools_files list.

New JS compiler standalone module added.

Drive-by: reformatted copy actions in devtools.gyp for better readability.

BUG=None
R=lushnikov@chromium.org

Review URL: https://codereview.chromium.org/143433002

git-svn-id: svn://svn.chromium.org/blink/trunk@165437 bbb929c8-8fbe-4397-9dbb-9b2b20218538