Use libprocessgroup to find cgroup v2 paths

Cgroup v2 paths are owned by libprocessgroup. Those paths can change
based on build flags, so paths generated outside of libprocessgroup may
not always be correct.

Bug: 382693152
Test: atest binderLibTest
Change-Id: Iefbf6716f657a6d2505cb760702de7401e220134

Author: tweej

libs/binder/tests/binderLibTest.cpp

@@ -335,7 +335,12 @@ class BinderLibTest : public ::testing::Test {
         }
 
         bool checkFreezeSupport() {
-            std::ifstream freezer_file("/sys/fs/cgroup/uid_0/cgroup.freeze");
+            std::string path;
+            if (!CgroupGetAttributePathForTask("FreezerState", getpid(), &path)) {
+                return false;
+            }
+
+            std::ifstream freezer_file(path);
             // Pass test on devices where the cgroup v2 freezer is not supported
             if (freezer_file.fail()) {
                 return false;