Use framework-res keep rules for system_server

The framework-res manifest defines a number of services implemented in
system_server. These required manual keep rules to prevent shrinking,
but now we can use the aapt-generated keep rules to achieve the same
result, without the maintenance burden.

A follow-up change will trim the existing keep rules to remove redundant
keeps, and plumb the same keep rules to other targets that define
system_server jars.

Bug: 272495195
Test: m + validate no net change to services.jar
Change-Id: Ibbb3ba47417ecadfae92764933761c4339ca6b35

services/Android.bp

@@ -59,7 +59,12 @@ system_optimized_java_defaults {
                 optimize: false,
                 shrink: true,
                 ignore_warnings: false,
-                proguard_flags_files: ["proguard.flags"],
+                proguard_flags_files: [
+                    "proguard.flags",
+                    // Ensure classes referenced in the framework-res manifest
+                    // and implemented in system_server are kept.
+                    ":framework-res{.aapt.proguardOptionsFile}",
+                ],
             },
             // Note: Optimizations are disabled by default if unspecified in
             // the java_library rule.