Setting Up Git: Unify ChromeOS instructions into Linux section

[miryarik]

Because

The ChromeOS Git installation instructions were isolated in their own section and used an out-dated workaround, which created redundancy and confusion for users. Since ChromeOS now comes with Linux Development Environment and APT can be used to install packages as one would on Debian, it makes sense to update the instructions and unify them under the existing Linux section for correctness and relevance.

This PR

• Moved ChromeOS-specific Git installation instructions into the Linux section
• Added a tip callout for ChromeOS users at the start of the Linux section
• Removed the standalone ChromeOS section to reduce duplication
• Included both recommended and legacy options for ChromeOS users within the Linux section

Issue

Closes #28232

Additional Information

Includes reference link to Google Support for Turning On Linux on ChromeOS.

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[xandora]

@miryarik After reviewing this PR, I think it might be better if we keep the ChromeOS dropdown section, but just update the method for installing Git.

We also don't really want to suggest that we provide support for older Chromebooks that don't have access to the Linux Dev Environment. When we brought Chromebooks on, it was purely because the Linux Dev Env was releasing soon and we had it as a beta. We didn't provide support for any Chromebook before that, and it's not something we want to start including.

If you can have another go to address this changes, we should be in a good place to get this merged.

[miryarik]

@xandora sure thing, i'll have another go. I'll rewrite the linux instructions and update the chromeos ones a bit. both in their separate sections as they are right now.