Patterns parsing: Add logEvent call to Listener.handlePatternVariable…

…DeclarationStatement.

Normally, listener methods call `LogEvent`.  This helps find bugs
where a listener that extends `Listener` doesn't implement a necessary
callback.

Bug: #50035
Change-Id: Ideac739d8d63cda2244572f7d1deb83dceeced37
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/272346
Commit-Queue: Paul Berry <[email protected]>
Reviewed-by: Konstantin Shcheglov <[email protected]>

pkg/_fe_analyzer_shared/lib/src/parser/listener.dart

@@ -2136,5 +2136,7 @@ class Listener implements UnescapeErrorListener {
   /// patterns accepted by the `outerPattern` grammar rule defined in the
   /// patterns spec.
   void handlePatternVariableDeclarationStatement(
-      Token keyword, Token equals, Token semicolon) {}
+      Token keyword, Token equals, Token semicolon) {
+    logEvent('PatternVariableDeclarationStatement');
+  }
 }