[REFACTOR] health 2.0: healthd_common -> libhealthloop

This change converts the original healthd_common.cpp to a
C++ class, HealthLoop, that manages the infinite loop in health-related
modules (charger, health HAL, healthd, etc.). By doing so, the global
static variables (including FDs and healthd_mode_ops) are cleaned up.

This helps us implement health HAL 2.1.

In order to support legacy modules (namely, healthd, charger, health HAL
2.0, which all depends on android.hardware.health@2.0-impl), a
healthd_common_adapter.cpp file is added to
android.hardware.health@2.0-impl, so that the following functions
in healthd/healthd.h continues to be implemented using the global
healthd_mode_ops:
    - healthd_register_event
    - healthd_battery_update_internal

Test: boot up the device and run VTS test on health HAL.
Bug: 137670450
Bug: 142260281
Change-Id: Iadcfc1315155404a3600f0e1219b5bc370d96409
diff --git a/health/utils/libhealthloop/Android.bp b/health/utils/libhealthloop/Android.bp
new file mode 100644
index 0000000..de0f24f
--- /dev/null
+++ b/health/utils/libhealthloop/Android.bp
@@ -0,0 +1,35 @@
+// Copyright (C) 2019 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+cc_library_static {
+    name: "libhealthloop",
+    vendor_available: true,
+    recovery_available: true,
+    srcs: [
+        "HealthLoop.cpp",
+        "utils.cpp",
+    ],
+    shared_libs: [
+        "libcutils",
+        "libbase",
+    ],
+    header_libs: [
+        "libbatteryservice_headers",
+        "libhealthd_headers",
+        "libutils_headers",
+    ],
+    export_include_dirs: [
+        "include",
+    ],
+}