Fix Map/Set creation via the API with nosnap build

Fix Map/Set creation via the API with nosnap build

The Map and Set maps get overwritten when collection.js executes, so in
a nosnap build we have to wait until it runs before we grab the maps.
To facilitate that, store the functions in the native context as well.

Review URL: https://codereview.chromium.org/1161363002

Cr-Commit-Position: refs/heads/master@{#28743}