test: convert most N-API tests from C++ to C

* Prefix functions with `static` to make them local
* Remove anonymous namespaces
* `nullptr` -> `NULL`
* .cc -> .c and update binding.gyp
* `static_cast<x>()` -> `(x)()`
* Replace `new`/`delete` with `malloc()`/`free()`
  (only in test_callback_scope)
* Move lambda out and convert to local function
  (only in test_callback_scope)
* Remove superfluous `#include <vector>`
  (only in test_callback_scope_recurse)

Some tests are best left as C++.

```bash
ls -l test/{node-api,js-native-api}/*/*.cc
```

for those remaining as C++ tests.

Signed-off-by: Gabriel Schulhof <gabriel.schulhof@intel.com>
PR-URL: https://github.com/nodejs/node/pull/34615


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>