✨ GitHub Copilot support

### Description

Add support for GitHub Copilot. It's possible to add support using https://github.com/TerminalFi/LSP-copilot as a base.

### Alternatives Considered

_No response_

### Additional Context

_No response_

### Screenshots

_No response_

Start by reviewing the CodeEdit repository and the proposed TerminalFi/LSP-copilot project to understand how GitHub Copilot support could fit into the macOS editor. Done means CodeEdit supports GitHub Copilot; the issue does not name specific files, entry points, tests, or acceptance details.

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