Fix protocol docs: diagnostics ranges are 0-based

All clients (emacs, vscode, intellij) send raw editor positions for
diagnostics, which are 0-based. Only the newer editor definition and
references locations are 1-based on the wire.

Author: ericdallo

docs/protocol.md

@@ -2386,7 +2386,8 @@ interface EditorDiagnostic {
     source: string;
 
     /**
-     * The diagnostic range (1-based).
+     * The diagnostic range (0-based, as editors report them natively;
+     * unlike editor definition/references locations, which are 1-based).
      */
     range: Range;