This lowers JSCreateFunctionContext nodes to call the above stub for
help with allocating function contexts when possible. It also contains
an implementation for inlined allocations of such contexts, which is
still behind a flag until inlined allocations are ready for prime time.

TEST=unittests/JSTypedLoweringTest.JSCreateFunctionContext
R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/1380113002

Cr-Commit-Position: refs/heads/master@{#31068}