Check that diagnostics generation works when running verify-round-trip

This allows us to reduce cases in which the parser is crashing during diagnostic generation.

Author: ahoppen

Sources/swift-parser-cli/swift-parser-cli.swift

@@ -133,6 +133,8 @@ class VerifyRoundTrip: ParsableCommand {
   ) throws {
     let tree = Parser.parse(source: source)
 
+    _ = ParseDiagnosticsGenerator.diagnostics(for: tree)
+
     let resultTree: Syntax
     if foldSequences {
       resultTree = foldAllSequences(tree).0