Reintroduce C++ support and add usage tests for C++ (#4)

Reviewed-on: #4
Co-authored-by: Abdelrahman <said.abdelrahman89@gmail.com>
Co-committed-by: Abdelrahman <said.abdelrahman89@gmail.com>

src/primitives/strings/str8/str8.c

@@ -28,6 +28,15 @@ RETURN_STR8:
   return str;
 }
 
+Str8 *wapp_str8_alloc_and_fill_buf(const Allocator *allocator, u64 capacity) {
+  Str8 *out = wapp_str8_alloc_buf(allocator, capacity);
+  if (out) {
+    memset(out->buf, 0, capacity);
+    out->size = capacity;
+  }
+  return out;
+}
+
 Str8 *wapp_str8_alloc_cstr(const Allocator *allocator, const char *str) {
   wapp_debug_assert(allocator != NULL && str != NULL, "`allocator` and `str` should not be NULL");