Instead of creating the SFIs during bootstrapping and storing on the
context, this patch just creates the SFIs on demand.

This patch saves 8 words per context, and several words per bound
function by not storing the SFI.

The created bound JSFunction is cached on the instance anyway, so it's
totally fine to take a small hit when creating the bound JSFunction.

Previously in the JS implementation, the creation of a bound function
was even slower as it was a lazy function that would have to parsed,
compiled and executed. So this is a step up in terms up perf and
memory.

Bug: v8:5751
Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: If3b8461d00e5b37567b34b236d44e14576b630ff
Reviewed-on: https://chromium-review.googlesource.com/1200006Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55566}