Add severity tracking to IssueInfo struct and factor failure summary logic into TestRunSummary type

Author: tienquocbui

Sources/Testing/Events/Recorder/Event.ConsoleOutputRecorder.swift

@@ -309,8 +309,7 @@ extension Event.ConsoleOutputRecorder {
 
     // Print failure summary when run ends
     if case .runEnded = event.kind {
-      let summary = _humanReadableOutputRecorder.generateFailureSummary(options: options)
-      if !summary.isEmpty {
+      if let summary = _humanReadableOutputRecorder.generateFailureSummary(options: options) {
         // Add blank line before summary and after summary for visual separation
         write("\n\(summary)\n")
       }