Rate limit dropbox entries in ActivityManagerService per process and add

a test for the rate limiting.

This is a direct cherrypick from master with no changes.

Design doc: go/apc-rate-limit-dropbox

Bug: 225173288
Test: atest DropboxRateLimiterTest
Change-Id: I08ccc151a3af867360ec8376725679bcfb92f4f6
(cherry picked from commit 13d85f0f)
Merged-In: I08ccc151a3af867360ec8376725679bcfb92f4f6