[libstatssocket] Added validation for adding new data into StatsEvent

Bug: 330054251
Test: atest StatsEventTest#TestHeapBufferOverflowError
Ignore-AOSP-First: security
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:4f6c56889356a5a422b59c71e9142875d00e43bf)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:e440696c4fd6d44d21451467294b3e31c6867e08)
Merged-In: I27c69d9875b494f98a2a961cdd4fe139cd809387
Change-Id: I27c69d9875b494f98a2a961cdd4fe139cd809387