Replacing NULL with nullptr in core/

[ Merge of http://go/wvgerrit/84647 ]
[ Merge of http://go/wvgerrit/84648 ]

Replacing most instances of C's NULL with C++'s nullptr.  Also changed
how a NULL check is performed on smart pointers.  They provided an
implicit boolean operator for null checks, meaning the underlying
pointer does not need to be compared directly (as it was in some places
before).

Note that clang-format has performed additional changes to some of the
test files that have not yet been formatted.

Bug: 120602075
Test: Linux and Android unittests
Change-Id: I06ddebe34b0ea6dfecedb5527e7e808e32f5269a

libwvdrmengine/cdm/core/include/buffer_reader.h

@@ -27,7 +27,7 @@ namespace wvcdm {
 class BufferReader {
  public:
   BufferReader(const uint8_t* buf, size_t size)
-      : buf_(buf), size_(buf != NULL ? size : 0), pos_(0) {}
+      : buf_(buf), size_(buf != nullptr ? size : 0), pos_(0) {}
 
   bool HasBytes(size_t count) const { return pos_ + count <= size_; }
   bool IsEOF() const { return pos_ >= size_; }