Allow `.cxx` and `.cc` extensions

[kittaakos]

Describe the request

This is the little sister task of arduino/arduino-cli#1149. Allow creating .cxx and .cc in IDE2.

Describe the current behavior

It's not possible.

Arduino IDE version

2.2.1

Operating system

macOS

Operating system version

13.5.2

Additional context

No response

Issue checklist

• I searched for previous requests in the issue tracker
• I verified the feature was still missing when using the latest nightly build
• My request contains all necessary details