The gameplay monitor wasn't being unloaded correctly in between levels. This meant that exit signals were not being sent, and entered signals for the new level were being missed.
This PR sends appropriate exit signals on unloading, and clear the data.
(cherry picked from commit 6c1e243fa2)
Fixes a bug whereby it read from the primary PVS in the gameplay monitor, using the size from the secondary PVS. This would read out of bounds and crash.
Removed debug code to update the gameplay monitor from the preview camera - this is no longer required.
Temporarily revert to the simple PVS generation method, because I've noticed a bug in the complex version, and the simple version is safer while I fix this.
