fix(completion): edge cases of operator completions (#15169)

# Description

Improves the completeness of operator completions.
Check the new test cases for details.

# User-Facing Changes

# Tests + Formatting

+4

# After Submitting

crates/nu-lsp/src/lib.rs

@@ -705,7 +705,8 @@ impl LanguageServer {
                             .map(|kind| match kind {
                                 SuggestionKind::Type(t) => t.to_string(),
                                 SuggestionKind::Command(cmd) => cmd.to_string(),
-                                SuggestionKind::Module => "".to_string(),
+                                SuggestionKind::Module => "module".to_string(),
+                                SuggestionKind::Operator => "operator".to_string(),
                             })
                             .map(|s| CompletionItemLabelDetails {
                                 detail: None,
@@ -754,6 +755,7 @@ impl LanguageServer {
                 nu_protocol::engine::CommandType::External => Some(CompletionItemKind::INTERFACE),
                 _ => None,
             },
+            SuggestionKind::Operator => Some(CompletionItemKind::OPERATOR),
             SuggestionKind::Module => Some(CompletionItemKind::MODULE),
         })
     }