UseCounter: Count ES6 modules instantiation

This should serve as a better proxy for measuring ES6 modules usage
in the wild.
Before this CL, we relied on kPrepareModuleScript, which only counts
ES6 module usage via <script type=module>, and no other invocation paths.
kInstantiateModuleScript will also cover module usage via dynamic import,
via workers, and others.

Bug: 594639
Change-Id: I5d1690fcfb7ea6ee9eac3beb22a4659a1410c561
Reviewed-on: https://chromium-review.googlesource.com/c/1314011
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Kouhei Ueno <kouhei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604842}
3 files changed