Creating a new RNG and replacing rand().

[ Merge of http://go/wvgerrit/84607 ]
[ Merge of http://go/wvgerrit/84608 ]

The primary goal is to replace the use of `rand()` with the random
number generators provided with the C++11 standard.

This simplified generator wraps some of the technical aspects of the
<random> library and provides an interface for uniformly distributed
integers.

As part of the `rand()` purge in the CDM, all uses of the C random int
function in `core()` have been removed.  Places that previously used
`rand()` now use `CdmRandom` facilities.

Test: Linux unittest and Android unittest
Bug: 130680365
Change-Id: Ica383870536ed462dbb80e630c2d66845e38b937

libwvdrmengine/cdm/test/Android.mk

@@ -36,6 +36,10 @@ test_src_dir := .
 test_main := ../core/test/test_main.cpp
 include $(LOCAL_PATH)/integration-test.mk
 
+test_name := cdm_random_unittest
+test_src_dir := ../util/test
+include $(LOCAL_PATH)/unit-test.mk
+
 test_name := cdm_session_unittest
 test_src_dir := ../core/test
 test_main := ../core/test/test_main.cpp