Add guidance for VS Code / Web IDE terms

What does this MR do?

Based on @brendan777's comments in !169195 (comment 2158840886), it's time to get some official guidance for VS Code / Web IDE terms into our style guide. (The Web IDE is based on VS Code, btw.) I'm currently migrating the VS Code extension's docs into the gitlab monolith as part of #493994.

Brendan's question was about the phrase command palette. The VS Code documentation (https://code.visualstudio.com/docs/getstarted/userinterface) uses title case to refer to UI elements.

• Do we want to do that as well?
• Do we want to bold these names? (I bolded them in this MR to nudge the conversation forward, but I think in the end we probably won't bold them.)

@ashrafkhamis will be interested in the outcome here, because he works on docs for the Web IDE.

Related issues

• Related to Track adding in version numbers to all images (#493994) where I'm tracking all the work
• Related to Add snippet-related items to VS Code page (!169195 - merged) where it came up in TW review.

Author's checklist

• Optional. Consider taking the GitLab Technical Writing Fundamentals course.
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  • Style Guide.
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• ~"frontend"
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These labels cause the MR to be added to code verification QA issues.

Reviewer's checklist

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If you aren't sure which tech writer to ask, use roulette or ask in the #docs Slack channel.

• If the content requires it, ensure the information is reviewed by a subject matter expert.
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