Add android.gsi.* keep rules to system server

These classes are statically linked both into the bootclasspath and
system server. Add an associated keep rule to avoid optimizing such
classes in system server, avoiding runtime issues where the class
signatures and APIs may differ from those in the framework, which take
precedence.

Also group related rules for similar bootclasspath conflicts in a single
section of the proguard config. A follow-up change will enable warnings
for such collisions, and also make it harder to introduce new violations
(by way of StrictPackagesJavaTest).

Bug: 222468116
Bug: 349245577
Test: atest CtsStrictJavaPackagesTestCases
Test: FULL_SYSTEM_OPTIMIZE_JAVA=true atest CtsStrictJavaPackagesTestCases
Test: FULL_SYSTEM_OPTIMIZE_JAVA=true + presubmit
Flag: EXEMPT bugfix
Change-Id: I017b360d3e4d62be2a07abd13340abb772d9cbbb