tools: apply more stringent lint rules for benchmark code

All benchmark code uses trailing commas on multi-line arrays and arrow
functions for anonymous callbacks. Apply lint rules to that effect.

benchmark/.eslintrc.yaml

@@ -0,0 +1,10 @@
+## Benchmark-specific linter rules
+
+rules:
+  comma-dangle: 
+    - error
+    - arrays: 'always-multiline'
+      objects: 'only-multiline'
+      imports: 'only-multiline'
+      exports: 'only-multiline'
+  prefer-arrow-callback: error