Introduce simplified BooleanToNumber operator.

R=titzer@chromium.org
TEST=cctest/test-simplified-lowering/LowerBooleanToNumber

Review URL: https://codereview.chromium.org/579723004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24009 ce2b1a6d-e550-0410-aec6-3dcde31c8c00