Lock the CoreSettings in ActivityThread separately

To fix a deadlock between the locks 'mResourceManager' and LoadedApk

Bug: 175361185
Test: atest FrameworksServicesTests:CoreSettingsObserverTest
Test: atest FrameworksCoreTests:ActivityThreadTest
Test: atest CtsGpuToolsHostTestCases:CtsRootlessGpuDebugHostTest
Test: Manual - adb shell am refresh-settings-cache
Change-Id: I283e7edb51ea1305a4beb31a4e0b5c751ccb8607