Add genrules for merged system server stubs

Re-land https://r.android.com/1596559 .

Bug: 177640454
Test: diff frameworks/base/services/api/current.txt \
out/soong/.intermediates/frameworks/base/api/services-system-server-current.txt/gen/system-server-current.txt

Merged-In: I021f59bb91572d28798a97ab8aa687b684599d6c
Change-Id: I5d5045f8d8f6b0ccdfb185582d1d4c4309937e6a
2 files changed