Add example sketches

[alnpokrovsky]

Currently the library does not include any bundled example sketches.

Due to the library's origin as part of the core, the examples were instead included in the "built-in" examples bundled with Arduino IDE:

https://github.com/arduino/arduino-examples/tree/main/examples/09.USB

This poses two problems:

• Users are accustomed to finding library examples via the File > Examples > <library name> menu path in the IDE
• The "built-in" examples are not be available for users of other development tools which provide the Mouse library (e.g., Arduino CLI, PlatformIO)