Replace typedefs in C++ with using declarations (#1339)

These are more readable than typedefs. C headers were left alone.

cscore/src/main/native/cpp/Frame.h

@@ -29,7 +29,7 @@ class Frame {
   friend class SourceImpl;
 
  public:
-  typedef uint64_t Time;
+  using Time = uint64_t;
 
  private:
   struct Impl {

cscore/src/main/native/cpp/Notifier.cpp

@@ -24,7 +24,7 @@ namespace {
 template <typename T>
 class UidVector {
  public:
-  typedef typename std::vector<T>::size_type size_type;
+  using size_type = typename std::vector<T>::size_type;
 
   size_type size() const { return m_vector.size(); }
   T& operator[](size_type i) { return m_vector[i]; }

cscore/src/main/native/cpp/default_init_allocator.h

@@ -14,7 +14,7 @@ namespace cs {
 // convert value initialization into default initialization.
 template <typename T, typename A = std::allocator<T>>
 class default_init_allocator : public A {
-  typedef std::allocator_traits<A> a_t;
+  using a_t = std::allocator_traits<A>;
 
  public:
   template <typename U>