Helper classes for IpcDataCache clients

Bug: 227653108

This adds a helper class that can reduce much of the boilerplate in
code that uses IpcDataCache (or the internal-only variant,
PropertyInvalidatedCache).  See the changes to DevicePolicyManager for
example usage.

Two PropertyInvalidatedCaches APIs are exposed for testing.  The
method createPropertyName() is changed so that apis like "Foo" are
converted to "foo", not "_foo".

Unit tests for the new behavior are added to IpcDataCacheTest.

This was manually tested by dumping the cache info from builds with
and without this change.  Special attention is paid to the
DevicePolicyManager caches.  The same caches were found (as identified
by their key and api) and the caches were enabled/disabled the same.

In the course of testing, multiple instances of DevicePolicyManager
caches were observed.  Cache performance is better if the caches are
static; making them static will be addressed in b/228452829.

Test:
 * atest FrameworksCoreTests:IpcDataCacheTest
 * atest FrameworksCoreTests:PropertyInvalidatedCacheTests
 * atest FrameworksServicesTests:DevicePolicyConstantsTest
 * atest FrameworksServicesTests:DevicePolicyEventLoggerTest
 * atest FrameworksServicesTests:DevicePolicyManagerServiceMigrationTest
 * atest FrameworksServicesTests:DevicePolicyManagerTest
 * atest FrameworksServicesTests:EnterpriseSpecificIdCalculatorTest
 * atest FrameworksServicesTests:OverlayPackagesProviderTest
 * atest FrameworksServicesTests:OwnersTest
 * atest FrameworksServicesTests:PolicyVersionUpgraderTest
 * atest FrameworksServicesTests:SecurityEventTest
 * atest FrameworksServicesTests:SystemUpdatePolicyTest
 * atest FrameworksServicesTests:TransferOwnershipMetadataManagerTest
 * atest MixedDeviceOwnerTest#testIsDeviceOrganizationOwnedWithManagedProfile
 * atest MixedDeviceOwnerTest#testSetKeyguardDisabledFeatures
 * atest MixedManagedProfileOwnerTest#testIsDeviceOrganizationOwnedWithManagedProfile
 * atest MixedManagedProfileOwnerTest#testNetworkLoggingDelegate
 * atest MixedManagedProfileOwnerTest#testSetKeyguardDisabledFeatures
 * atest OrgOwnedProfileOwnerTest#testIsDeviceOrganizationOwnedWithManagedProfile
 * atest OrgOwnedProfileOwnerTest#testNetworkLoggingDelegate
 * atest OrgOwnedProfileOwnerTest#testSetKeyguardDisabledFeatures
 * atest android.devicepolicy.cts.DevicePolicyManagerTest
 * atest android.devicepolicy.cts.NetworkLoggingTest
 * atest com.android.cts.devicepolicy.DeviceOwnerTest#testAdminActionBookkeeping

Change-Id: I2f4fe4ed25db5fb3100334b9d2ce748ee928c10d