Delegate showing help to the back end process.

[tsmaeder]

What it does

Fixes #13727

The approach is to add non-functional cli contributions for any arguments that concern only the electron-main process. Currently, we have a bit of confusion between the theia cli tool, which is mostly a development-time tool (theia build, etc.) and the actual Theia application executable (TheiaIde.exe). It would probably make sense to evolve the architecture in a way that all possible command line options are available to all "customer-facing" cli tools and can be selectively forwarded to the back-end, plugin-process and any other processes making up Theia.

Contributed on behalf of STMicroelectronics

How to test

The closest equivalent to what the TheiaIDE.exe does is the "Launch electron back end" launch configuration. To test, you can add parameters after the initial . parameter (which is a parameter to Electron). One can also use npx theia start <...params> on the command line in the electron or browser example.
In these way, test that the help commands output reasonable advice and that start parameters are properly handled.

Follow-ups

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[msujew]

Looks good to me 👍

I'm getting a bit of superfluous output before the --help command, but similarly to the server case, there's probably no easy way around this:

Showing splash screen
SplashScreen options { content: 'resources/theia-logo.svg', height: 90 }