Start diagnostic group_id at 1 to handle non LS diagnostics (#22694)

In particular, `DiagnosticPopover` both:

* Supports moving the selection to a diagnostic when clicked, based on
`group_id`

* Provides Diagnostic values with `group_id: 0` providing informztion on
hover about invisible characters.

So, clicking such a popover would navigate to the very first error
produced by a language server. Really not a big deal of course, but
seems good to fix as it might result in surprising behavior in other
future circumstances

Release Notes:

- N/A

crates/collab/src/tests/integration_tests.rs

@@ -4065,7 +4065,7 @@ async fn test_collaborating_with_diagnostics(
                 DiagnosticEntry {
                     range: Point::new(0, 4)..Point::new(0, 7),
                     diagnostic: Diagnostic {
-                        group_id: 2,
+                        group_id: 3,
                         message: "message 1".to_string(),
                         severity: lsp::DiagnosticSeverity::ERROR,
                         is_primary: true,
@@ -4075,7 +4075,7 @@ async fn test_collaborating_with_diagnostics(
                 DiagnosticEntry {
                     range: Point::new(0, 10)..Point::new(0, 13),
                     diagnostic: Diagnostic {
-                        group_id: 3,
+                        group_id: 4,
                         severity: lsp::DiagnosticSeverity::WARNING,
                         message: "message 2".to_string(),
                         is_primary: true,