JNI Zero: Add support for @JniType("std::map<>")

Serializes the Map to an Object[], and then populates a std::map (or
similar).

Bug: 326110639
Change-Id: Iaa72e11ebac6c11a711845e99c98551969a7351f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5615691


Commit-Queue: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1313601}