Refine system service proguard rules

Refine proguard rules for system services to prepare for rolling out
full system server R8 optimization.

Added proguard rules to keep auto-generated Java aconfig flags to
prevent Flag function from being inlined / removed since R8 do not have
context on flags that are referenced outside of the module.

Bug: 313546597
Change-Id: I184cd7a79acc7fa2d9db66438df1f0b50d951fd9
Test: Local build and boot with full system server optimization