IDE startup theme based on OS theme

[francescospissu]

Motivation

The theme of the IDE on first launch should be the same as the OS.

Change description

Implemented a patch that replaces the ThemeService.get().loadUserTheme(); function at startup by directly setting the theme based on the OS theme.
For all subsequent starts of the IDE the theme applied will be the last one set by the user.

Other information

With the current version of Theia adopted (1.25) it is not possible to extend the ThemeService, it will be possible starting from Theia 1.27.
Once the version of Theia is updated, this patch will be removed and this functionality will be implemented via dependency injection.

Closes #530.

Reviewer checklist

• PR addresses a single concern.
• The PR has no duplicates (please search among the Pull Requests before creating one)
• PR title and description are properly filled.
• Docs have been added / updated (for bug fixes / features)

[kittaakos]

This should work: fspissu/startup-theme...kittaakos:arduino-ide:startup-theme-2.
If you have any questions, let me know.

Update: I think the long-term goal is to support dark and light themes in Theia natively and not customize the ThemeService with injection.

[francescospissu]

Thanks for your support @kittaakos. In a later step I can create a contribution on Theia to achieve this directly there.

[kittaakos]

Thank you! I did not check the behavior but the code changes look good to me.

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Could you please ask the Theia community why we need this hack?

[AlbyIanna]

Nice hack 😎

I tested it on MacOS and it works perfectly.

LGTM 🚀