Assembly language file extension has the wrong case

[per1234]

Describe the bug
The Arduino build system requires assembly language files to use the .S file extension but the "New Tab" dialog only allows .s. Files using the .s extension are not compiled.

To Reproduce

1. Click the downward pointing triangle button on the right side of the tab bar.
2. Click "New Tab"
3. In the "Name for new file" dialog, type "Foo.S". - ".S is not a valid file extension." is shown and the "OK" button is disabled.

Expected behavior
The .S file extension to be allowed and the .s extension prohibited by the "New Tab" and "Rename" dialogs of the tab control menu.

Desktop (please complete the following information):

• OS: Windows 10
• Version: 2.0.0-beta.3-nightly.20210313
  Date: 2021-03-13T03:11:23.309Z
  CLI Version: 0.16.1 alpha [76f55490]

Additional context
Reference from the Arduino Sketch Specification: https://arduino.github.io/arduino-cli/latest/sketch-specification/#additional-code-files

I believe the relevant code is here:

arduino-ide/arduino-ide-extension/src/common/protocol/sketches-service.ts

Lines 89 to 90 in eadc993

	export const SOURCE = ['.c', '.cpp', '.s'];
	export const ADDITIONAL = ['.h', '.c', '.hpp', '.hh', '.cpp', '.s', '.json'];

[kittaakos]

Monkey see monkey do 😊 Thanks for bringing this up.

Let's check if we have to adjust anything in the CLI:

• https://github.com/arduino/arduino-cli/blob/414ab001a235c213f96e00f185f082783118e109/arduino/globals/globals.go#L38
• https://github.com/arduino/arduino-cli/blob/414ab001a235c213f96e00f185f082783118e109/arduino/globals/globals.go#L45
• https://github.com/arduino/arduino-cli/blob/414ab001a235c213f96e00f185f082783118e109/legacy/builder/builder.go#L34-L35
• https://github.com/arduino/arduino-cli/blob/414ab001a235c213f96e00f185f082783118e109/legacy/builder/create_cmake_rule.go#L35