rust-analyzer cleanup and hover support

This merge request tries to cleanup the new rust analyzer plugin aswell as support highlighter and hover features of GNOME Builder

• guard and contracts for functions
• transfer notification should show when its done
• translation is missing for user visible messages
• investigate runtime warning (cancellable + set_parent)
• hover support
  • support MarkupContent according to LSP specification https://microsoft.github.io/language-server-protocol/specifications/specification-current/#markupContent
  • hover plugin enhancements for LSP client
• highlighter support
• rename support
  • enhanced lsp implementation to support documentChanges also (see https://microsoft.github.io/language-server-protocol/specifications/specification-current/#workspaceEdit)
  • show symbol which should be renamed in popup
  • rust analyzer rename provider
• symbol search support
• preferences addon for configuration of cargo check command (enables cargo clippy)