Option to disable decimal separator in built-in Calculator plugin

**Describe the solution you'd like**

Add option to disable decimal separator in built-in Calculator plugin.

**Describe alternatives you've considered**

Add "None" to the drop down selection list.

**Additional context**

Inspect the built-in Calculator plugin and the settings dropdown shown in the issue image to find where the decimal separator is configured. Add a None option that disables the separator, then verify the setting through the calculator plugin's normal input and output behavior.

Written by the indexing model from the issue text.