PG-1892 Move InternalKey to common file

This structure seems generally useful and doesn't belong with the
relation key code.

contrib/pg_tde/src/include/access/pg_tde_keys_common.h

@@ -3,9 +3,6 @@
 
 #include "catalog/tde_principal_key.h"
 
-#define INTERNAL_KEY_LEN 16
-#define INTERNAL_KEY_IV_LEN 16
-
 #define MAP_ENTRY_IV_SIZE 16
 #define MAP_ENTRY_AEAD_TAG_SIZE 16
 

contrib/pg_tde/src/include/access/pg_tde_tdemap.h

@@ -4,12 +4,7 @@
 #include "storage/relfilelocator.h"
 
 #include "access/pg_tde_keys_common.h"
-
-typedef struct InternalKey
-{
-	uint8		key[INTERNAL_KEY_LEN];
-	uint8		base_iv[INTERNAL_KEY_IV_LEN];
-} InternalKey;
+#include "encryption/enc_tde.h"
 
 extern void pg_tde_save_smgr_key(RelFileLocator rel, const InternalKey *key);
 extern bool pg_tde_has_smgr_key(RelFileLocator rel);

contrib/pg_tde/src/include/access/pg_tde_xlog_keys.h

@@ -4,6 +4,7 @@
 #include "access/xlog_internal.h"
 
 #include "access/pg_tde_keys_common.h"
+#include "access/pg_tde_tdemap.h"
 
 typedef enum
 {

contrib/pg_tde/src/include/encryption/enc_tde.h

@@ -5,7 +5,14 @@
 #ifndef ENC_TDE_H
 #define ENC_TDE_H
 
-#include "access/pg_tde_tdemap.h"
+#define INTERNAL_KEY_LEN 16
+#define INTERNAL_KEY_IV_LEN 16
+
+typedef struct InternalKey
+{
+	uint8		key[INTERNAL_KEY_LEN];
+	uint8		base_iv[INTERNAL_KEY_IV_LEN];
+} InternalKey;
 
 extern void pg_tde_generate_internal_key(InternalKey *int_key);
 extern void pg_tde_stream_crypt(const char *iv_prefix,