GraphicsEnv: refactor to unify the debuggable logic

By default, PR_SET_DUMPABLE is 0 for zygote spawned apps, except in the
following circumstances:
1. ro.debuggable=1 (global debuggable enabled, i.e., userdebug or eng builds).
2. android:debuggable="true" in the manifest for an individual application.
3. An app which explicitly calls prctl(PR_SET_DUMPABLE, 1).
4. GraphicsEnv calls prctl(PR_SET_DUMPABLE, 1) in the presence of
   <meta-data android:name="com.android.graphics.injectLayers.enable"
              android:value="true"/>
   in the application manifest.

So checking both ro.debuggable=1 and PR_GET_DUMPABLE is redundant.

Bug: 144186877
Test: CtsAngleIntegrationHostTestCases
Test: CtsRootlessGpuDebugHostTest
Change-Id: I934f64315b67db77ee2c2a9dff50fb23bc0a546a
diff --git a/libs/graphicsenv/GraphicsEnv.cpp b/libs/graphicsenv/GraphicsEnv.cpp
index 2859111..354703b 100644
--- a/libs/graphicsenv/GraphicsEnv.cpp
+++ b/libs/graphicsenv/GraphicsEnv.cpp
@@ -124,12 +124,8 @@
     return env;
 }
 
-int GraphicsEnv::getCanLoadSystemLibraries() {
-    if (property_get_bool("ro.debuggable", false) && prctl(PR_GET_DUMPABLE, 0, 0, 0, 0)) {
-        // Return an integer value since this crosses library boundaries
-        return 1;
-    }
-    return 0;
+bool GraphicsEnv::isDebuggable() {
+    return prctl(PR_GET_DUMPABLE, 0, 0, 0, 0) > 0;
 }
 
 void GraphicsEnv::setDriverPathAndSphalLibraries(const std::string path,