Revert "Merge "Revert "Use aidl::nullable for nullable type in C++"" into...

Revert "Merge "Revert "Use aidl::nullable for nullable type in C++"" into rvc-dev-plus-aosp am: 9beacac0 am: bd9b7af3 am: ec09e10c"

This reverts commit b1d388c7.

Reason for revert: Unintended revert got merged.

Change-Id: I85637ae4e88a9dcd233b3c17c6030fb726d5681f

Exempt-From-Owner-Approval: reverting unintended revert