Rename method CanUseKey for clarity

[ Merge of http://go/wvgerrit/60240 ]

Since the method is not a general purpose check and only verifies that
the key can be used for a given security level the method
has been renamed PolicyEngine::CanUseKeyForSecurityLevel.

Bug: 115701771
Test: WV unit/integration tests
Change-Id: Icd6789538bb709d2a48c67bbd7bc810f4b000e14

libwvdrmengine/cdm/core/src/cdm_session.cpp

@@ -588,7 +588,8 @@ CdmResponseType CdmSession::Decrypt(const CdmDecryptionParameters& params) {
         return INSUFFICIENT_OUTPUT_PROTECTION;
       return NEED_KEY;
     }
-    if (!policy_engine_->CanUseKey(*params.key_id, security_level_)) {
+    if (!policy_engine_->CanUseKeyForSecurityLevel(*params.key_id,
+                                                   security_level_)) {
       return KEY_PROHIBITED_FOR_SECURITY_LEVEL;
     }
   }

libwvdrmengine/cdm/core/src/policy_engine.cpp

@@ -314,7 +314,7 @@ CdmResponseType PolicyEngine::QueryKeyAllowedUsage(
   return KEY_NOT_FOUND_1;
 }
 
-bool PolicyEngine::CanUseKey(
+bool PolicyEngine::CanUseKeyForSecurityLevel(
     const KeyId& key_id,
     CdmSecurityLevel security_level) {