Clean up CdmEngine logs.

[ Merge of http://go/wvgerrit/121568 ]

The CdmEngine logs had both too much and too little information.

Since our logging has been enabled to print function names natively,
many of the log information has become superfluous.  Needless
information has been removed, and many of the important INFO logs have
been reduced to only the information not present in the function name.

Some of the INFO and ERROR logs were missing identifiers to match
failures with the same session request should the failures take more
than a few milliseconds to occur.  CDM session IDs and key set IDs
have been included in all the logs that _appeared_ to have a slow
operation between the top of the method and log.

To help make enum values more readable, several enums-to-string
functions have been implemented.  These converters are intended for
INFO logging and as such, do not log any addition information should
the enum be out of range.

To help make empty and null identifiers more readable in the logs,
empty strings will be logged as <empty> and null strings will be
logged as <null>.

While working through the "cdm_engine.cpp" file, a few minor changes
have been made:
- Adjust if statements to match with Google C++ style guidelines
  - Skipped anything that was not obvious
- Added a const qualifier to variables where appropriate
- Moved some null checks to the top of the method
  - Only where sequence is non-critical to normal operation
- Removed unnecessary string to vector to string conversions
- Reject empty |force_session_id|
  - Already enforced on CE CDM code and not uesd on Android

Bug: 183576879
Test: CE CDM unittests
Change-Id: Id165373055f7ce6097c93c48f84af74bd353c8cb

libwvdrmengine/cdm/Android.bp

@@ -61,6 +61,7 @@ cc_library_static {
         CORE_SRC_DIR + "/privacy_crypto_boringssl.cpp",
         CORE_SRC_DIR + "/service_certificate.cpp",
         CORE_SRC_DIR + "/usage_table_header.cpp",
+        CORE_SRC_DIR + "/wv_cdm_types.cpp",
         SRC_DIR + "/wv_content_decryption_module.cpp",
         METRICS_SRC_DIR + "/attribute_handler.cpp",
         METRICS_SRC_DIR + "/counter_metric.cpp",