GraphicsEnv: Fix isDebuggable

Update the logic used in GraphicsEnv to decide whether shared objects
can be inserted into the process.  This is used by Vulkan layers,
GLES layers, and ANGLE when deciding whether libraries from outside
packages can be used.

The new logic doesn't just use PR_GET_DUMPABLE which is no longer set
by default in platform debug builds. It also incorporates
ANDROID_DEBUGGABLE, which is defined when `debuggable` is true in
Android.bp. This happens for eng or userdebug builds of the platform.

The use of `debuggable` is the replacement for reading ro.debuggable
which can no longer be read at runtime (see b/193912100).

Tested with:
export APP_PACKAGE=<app from Play Store>
adb shell settings put global angle_debug_package org.chromium.angle
adb shell settings put global angle_gl_driver_selection_pkgs $APP_PACKAGE
adb shell settings put global angle_gl_driver_selection_values angle

Test: Released app able to load from angle_debug_package on userdebug
Test: Released app cannot use angle_debug_package on user build
Bug: b/253678459
Change-Id: I3dda4258e23871ee2fab2cf5ba367612e00de0e2
diff --git a/libs/graphicsenv/GraphicsEnv.cpp b/libs/graphicsenv/GraphicsEnv.cpp
index 4a0a839..5f5f85a 100644
--- a/libs/graphicsenv/GraphicsEnv.cpp
+++ b/libs/graphicsenv/GraphicsEnv.cpp
@@ -126,7 +126,20 @@
 }
 
 bool GraphicsEnv::isDebuggable() {
-    return prctl(PR_GET_DUMPABLE, 0, 0, 0, 0) > 0;
+    // This flag determines if the application is marked debuggable
+    bool appDebuggable = prctl(PR_GET_DUMPABLE, 0, 0, 0, 0) > 0;
+
+    // This flag is set only in `debuggable` builds of the platform
+#if defined(ANDROID_DEBUGGABLE)
+    bool platformDebuggable = true;
+#else
+    bool platformDebuggable = false;
+#endif
+
+    ALOGV("GraphicsEnv::isDebuggable returning appDebuggable=%s || platformDebuggable=%s",
+          appDebuggable ? "true" : "false", platformDebuggable ? "true" : "false");
+
+    return appDebuggable || platformDebuggable;
 }
 
 void GraphicsEnv::setDriverPathAndSphalLibraries(const std::string path,