Clear Local Cache while persistenceEnabled is turned on

## What feature would you like to see?

A function to clear the local persistence Cache for realtime database and firestore when persistenceEnabled is turned on.

`FirbaseDatabase.getInstance().clearLocalCache()`

The functions should drop all rows in the SQL Database Cache and also clear the write-ahead-log file.

## How would you use it?

In our app, we are using user-specific database queries. When a user logging out and the other user is logged in. Anyone with root access to device storage can read personal data of a logged out user. We would clear the cache with every logout.