@@replace has a pretty complex implementation, taking different paths
for various situations (e.g.: global/nonglobal regexp, functional/string
replace argument, etc.). Each of these paths must implement similar
logic for calling into the RegExpBuiltinExec spec operation, and many
paths get this subtly wrong.

This CL fixes a couple of issues related to the way @@replace handles lastIndex:
* All paths now respect lastIndex when calling into exec (some used to assume 0).
* lastIndex is now advanced after a successful match for sticky regexps.
* lastIndex is now only reset to 0 on failure for sticky regexps.

BUG=v8:5361

Review-Url: https://codereview.chromium.org/2685183003
Cr-Commit-Position: refs/heads/master@{#43234}