docs: update integrations section

[mcecode]

Issues

Not an issue, but a discussion on #710.

Description

• Rearrange integrations section's navigation (language server which powers editor integrations > editors with official plugins > editors that directly integrate with harper-ls > editors with third-party/community plugins)
• Transfer VS Code readme info to official docs
• Transfer VS Code development guide to official docs
• Remove non-Neovim specific installation methods in the Neovim page
• Transfer the configuration section explanations from the Neovim page to a new configuration section in the language server page
• Add link to language server installation instructions and sample config in the Helix page
• Add link to language server installation instructions and sample config in the Emacs page