Add tab size preference settings

[novialriptide]

Closes #15561

Description

• Mimics the functionality of GitHub's existing tab size preference setting. https://github.com/settings/appearance

Screenshots

Release notes

Notes: Added tab size preferences

Additional Information

I actually need help finalizing this... once the user has chosen a tab size, they need to manually reload the page in order to see the new changes and I spent around 30 minutes trying to find how to refresh the content but failed to do so. I was wondering if any of the experienced developers could help assist me?

[angusdev]

Need to consider tab stop instead of just replace with spaces. See below screen (first is production version, second is the PR version). Although the current behaviour also has bug, it should skip the (+) sign when calculating tab stop.

[novialriptide]

@angusdev

Thanks for noticing, the school semester is about to start soon 🥲, but I'll work on it in a bit.

[sergiou87]

Hey @novialriptide !! Thank you for your contribution 🙇‍♂️

We (the Desktop team) chatted about this today and think it'd be a nice addition, but just as github.com does, it shouldn't be in the diff viewer. Instead, it should be in some appearance / diff settings in the app settings dialog. Where exactly is hard to tell, since we have many settings already, but something we'd rather discuss (and agree) in the linked issue #15561 before any attempt of implementation is made.

Just to be clear, the reason we want to move the conversation to #15561 until all the details are agreed, is to avoid having too much noise in the PR list: we have too many PRs open and it's hard to keep up, especially if they require some discussion that could take days or weeks (we're a pretty small team 😳 ). So we're gonna close this PR and it can be reopened once we all agree on what will be done.

Sorry for any inconvenience and thank you again for your work! ❤️