API: Refactor: Add macro infrastructure for typed arrays

- Add macros supporting typed arrays in the remote API
- Refactor StringArray-related functions on top of the new macros

src/nvim/api/private/defs.h

@@ -34,10 +34,7 @@ REMOTE_TYPE(Tabpage);
 
 typedef struct object Object;
 
-typedef struct {
-  String *items;
-  size_t size;
-} StringArray;
+TYPED_ARRAY_OF(String);
 
 typedef struct {
   Integer row, col;