Add basic handling for entitlement keys in a license.

Merge from Widevine repo of http://go/wvgerrit/41834

Key rotation is not yet supported.

The key statuses are updated from a license. The
mechanism expects content keys tro come in a license.
For entitlement licenses, the content keys come in the
init_data.

This code does not yet support the key rotation event.
(A new pssh with wrapped keys is a passed to the cdm)
The policy engine/key status mechanism needs to be
updated to handle updated from the init_data.

For now, the cdm builds a license with a key container
with the content keys and used that to call
PolicyEngine::SetLicense to setup the policy engine
and key statuses.

Bug: 64003606
Bug: 70334840

Test: In child CL
Change-Id: Ibf46a18f5321cab4ff6f1778ba30527942c8021f

libwvdrmengine/cdm/Android.mk

@@ -35,6 +35,7 @@ LOCAL_SRC_FILES := \
     $(CORE_SRC_DIR)/content_key_session.cpp \
     $(CORE_SRC_DIR)/crypto_session.cpp \
     $(CORE_SRC_DIR)/device_files.cpp \
+    $(CORE_SRC_DIR)/entitlement_key_session.cpp \
     $(CORE_SRC_DIR)/initialization_data.cpp \
     $(CORE_SRC_DIR)/license.cpp \
     $(CORE_SRC_DIR)/license_key_status.cpp \