feat(c++): specify underlying types for enums in fwd.h (#811)

* updated types to platform independent types

* updated types

* removed forward declaration for Type class

* Apply clang-format and cpplint fixes

* Format C++ code with clang-format-8

* formatted with clang-format-8 to meet github action pipeline

Author: devadhe sb

cpp/src/graphar/fwd.h

@@ -70,16 +70,15 @@ class FileSystem;
 
 /** Type of vertex id or vertex index. */
 using IdType = int64_t;
-enum class Type;
 class DataType;
 /** Defines how multiple values are handled for a given property key */
-enum Cardinality { SINGLE, LIST, SET };
+enum Cardinality : int32_t { SINGLE, LIST, SET };
 /** Type of file format */
-enum FileType { CSV = 0, PARQUET = 1, ORC = 2, JSON = 3 };
-enum SelectType { PROPERTIES = 0, LABELS = 1 };
+enum FileType : int32_t { CSV = 0, PARQUET = 1, ORC = 2, JSON = 3 };
+enum SelectType : int32_t { PROPERTIES = 0, LABELS = 1 };
 /** GetChunkVersion: V1 use scanner, V2 use FileReader */
-enum GetChunkVersion { AUTO = 0, V1 = 1, V2 = 2 };
-enum class AdjListType : uint8_t;
+enum GetChunkVersion : int32_t { AUTO = 0, V1 = 1, V2 = 2 };
+enum class AdjListType : int32_t;
 
 template <typename T>
 class Array;

cpp/src/graphar/types.h

@@ -36,7 +36,7 @@ class DataType;
 namespace graphar {
 
 /** @brief Main data type enumeration. */
-enum class Type {
+enum class Type : int32_t {
   /** Boolean */
   BOOL = 0,
 
@@ -170,7 +170,7 @@ class Date {
 };
 
 /** Adj list type enumeration for adjacency list of graph. */
-enum class AdjListType : std::uint8_t {
+enum class AdjListType : std::int32_t {
   /// collection of edges by source, but unordered, can represent COO format
   unordered_by_source = 0b00000001,
   /// collection of edges by destination, but unordered, can represent COO