ESM Support

[dsanders11]

With ESM support coming to Electron 28, it would be nice to have support for main.mjs in Fiddle when that release happens. Rough sketch of what I think is necessary to support it.

• Add support for .mjs as a file extension
• Support either main.js or main.mjs for main process code
• Smooth out the UX
  • Don't allow both main.js and main.mjs to exist in a Fiddle
  • Consider whichever is present to be the required file
  • Show a warning to the user if they're trying to use main.mjs in a version before 28

Bonus points UX: Add a "Convert to ESM" button to the context menu when you right click main.js

[bnb]

Add support for .mjs as a file extension

is .cjs also already supported? Worth doing if not already.

[dsanders11]

is .cjs also already supported? Worth doing if not already.

Fair point. It is not, at the moment only .js, .html, and .css extensions are supported. Shouldn't be much extra work to toss in .cjs when refactoring to support alternatives to main.js as the main entrypoint.