This is the mirror image of #2170.

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- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
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Add `default_converter` argument to `to_js` and `toJs`. This is the mirror image of #2170.

### Checklists

<!-- Note on checklists:
     If you think some of these steps are not necessary for your PR,
     just remove those checkboxes, or mark them as checked. Otherwise,
     if some checkboxes are left unmarked, we might assume that your PR
     is not ready to be merged and we might keep you waiting -->

- [x] Add a [CHANGELOG](https://github.com/pyodide/pyodide/blob/main/docs/project/changelog.md) entry
- [x] Add / update tests
- [x] Add new / update outdated documentation

ac_cv_file__dev_ptmx=no
ac_cv_file__dev_ptc=no
ac_cv_func_dlopen=yes
ac_cv_lib_socket_socket=no
ac_cv_header_linux_vm_sockets_h=yes
ac_cv_little_endian_double=yes
ax_cv_c_float_words_bigendian=no

ac_cv_file__dev_ptmx=no
ac_cv_file__dev_ptc=no
ac_cv_func_dlopen=yes
ac_cv_lib_socket_socket=no
ac_cv_header_linux_vm_sockets_h=yes
ac_cv_little_endian_double=yes
ax_cv_c_float_words_bigendian=no
