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/core/include/cdm_engine.h

@@ -392,8 +392,6 @@ class CdmEngine {
   Clock clock_;
   std::string spoid_;
 
-  static bool seeded_;
-
   // usage related variables
   std::unique_ptr<CdmSession> usage_session_;
   std::unique_ptr<UsagePropertySet> usage_property_set_;