[WIP] Set up Copilot instructions for repository

[Copilot]

Thanks for assigning this issue to me. I'm starting to work on it and will keep this PR's description up to date as I form a plan and make progress.

Original prompt

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This section details on the original issue you should resolve

<issue_title>✨ Set up Copilot instructions</issue_title>
<issue_description>Configure instructions for this repository as documented in Best practices for Copilot coding agent in your repository.

This repo is my personal fork of VScode that I will be using to contribute PR's to the offical Microsoft vscode repo. Please reinforce coding and testing standards for the VSCode project that you know of or are in the CONTRIBUTING.md file in the project.

Also include instructions specifically how agents can write and test against the repo, especially tips for writing and testing Extensions.... Its about to get Inception-y in here :-)

</issue_description>

<agent_instructions>This repo is my personal fork of VScode that I will be using to contribute PR's to the offical Microsoft vscode repo. Please reinforce coding and testing standards for the VSCode project that you know of or are in the CONTRIBUTING.md file in the project.

Also include instructions specifically how agents can write and test against the repo, especially tips for writing and testing Extensions.... Its about to get Inception-y in here :-)
</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes ✨ Set up Copilot instructions #6

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✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

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