Increment IV in WVCryptoPlugin

WVCryptoPlugin was not properly implementing part of its responsibilities to
AES-CTR in ISO-CENC.  Specifically, it was not incrementing the IV after each
block.

Also, I have greatly expanded the unit tests for decrypt() to catch more edge
cases.

This change fixes the two failing test vectors in the Java integration tests.

Copied from https://widevine-internal-review.googlesource.com/#/c/5123/2

Bug: 8656421
Change-Id: If935edbf01068f5b0d5254b4e657057ef57d8fcf

libwvdrmengine/mediacrypto/include/WVCryptoPlugin.h

@@ -36,6 +36,7 @@ class WVCryptoPlugin : public android::CryptoPlugin {
   const wvcdm::CdmSessionId mSessionId;
 
   wvcdm::CdmSessionId configureTestMode(const void* data, size_t size);
+  static void incrementIV(uint64_t increaseBy, std::vector<uint8_t>* ivPtr);
 };
 
 } // namespace wvdrm