Disable in_app_purchase event

Feature request: disable auto logging of in_app_purchase. Now it logs prices with taxes. It breaks analytics and iTunes/Google has different in reports.

No file or test is named. Start by locating the Firebase Analytics C++ entry point that automatically emits the in_app_purchase event, then inspect the platform-specific purchase and reporting paths described in the issue. Done means automatic logging can be disabled without affecting other analytics behavior, with the relevant tests confirming the result.

Written by the indexing model from the issue text.