Separate out macOS and Linux keymaps (#13792)

Release Notes:

- Added Linux-Specific keymaps for JetBrains, Atom and Sublime Text
- Improved MacOS-specific keymaps for JetBrains and Atom
- Improved Linux default keymap (VSCode compatibility)
- Windows now uses same keymap as Linux

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Co-authored-by: Peter Tripp <peter@zed.dev>