Fix data type error in AIDL

utf8InCpp string should not be used to pass arbitrary data, as it drops
invalid chars during utf8-utf16 conversion.
byte[] is the correct type to use.

Bug: 250401609
Test: atest libgui_test libsurfaceflinger_unittest SurfaceFlinger_test
Change-Id: Ia1bf7e2cdc134a392d7b4edace9b2799a4c0d23b