Add benchmark script

The current build setup doesn't seem to have a concept for benchmark
scripts, so for now you'll have to run it with something like ts-node.

extensions/ql-vscode/test/benchmarks/jsonl-reader.bench.ts

@@ -0,0 +1,73 @@
+import { readFile } from "fs-extra";
+import { readJsonlFile } from "../../src/common/jsonl-reader";
+import { performance } from "perf_hooks";
+import { join } from "path";
+
+/** An "obviously correct" implementation to test against. */
+async function readJsonlReferenceImpl<T>(
+  path: string,
+  handler: (value: T) => Promise<void>,
+): Promise<void> {
+  const logSummary = await readFile(path, "utf-8");
+
+  // Remove newline delimiters because summary is in .jsonl format.
+  const jsonSummaryObjects: string[] = logSummary.split(/\r?\n\r?\n/g);
+
+  for (const obj of jsonSummaryObjects) {
+    const jsonObj = JSON.parse(obj) as T;
+    await handler(jsonObj);
+  }
+}
+
+type ParserFn = (
+  text: string,
+  callback: (v: unknown) => Promise<void>,
+) => Promise<void>;
+
+const parsers: Record<string, ParserFn> = {
+  readJsonlReferenceImpl,
+  readJsonlFile,
+};
+
+async function main() {
+  const args = process.argv.slice(2);
+  const file =
+    args.length > 0
+      ? args[0]
+      : join(
+          __dirname,
+          "../unit-tests/data/evaluator-log-summaries/bad-join-order.jsonl",
+        );
+  const numTrials = args.length > 1 ? Number(args[1]) : 100;
+  const referenceValues: any[] = [];
+  await readJsonlReferenceImpl(file, async (event) => {
+    referenceValues.push(event);
+  });
+  const referenceValueString = JSON.stringify(referenceValues);
+  // Do warm-up runs and check against reference implementation
+  for (const [name, parser] of Object.entries(parsers)) {
+    const values: unknown[] = [];
+    await parser(file, async (event) => {
+      values.push(event);
+    });
+    if (JSON.stringify(values) !== referenceValueString) {
+      console.error(`${name}: failed to match reference implementation`);
+    }
+  }
+  for (const [name, parser] of Object.entries(parsers)) {
+    const startTime = performance.now();
+    for (let i = 0; i < numTrials; ++i) {
+      await Promise.all([
+        parser(file, async () => {}),
+        parser(file, async () => {}),
+      ]);
+    }
+    const duration = performance.now() - startTime;
+    const durationPerTrial = duration / numTrials;
+    console.log(`${name}: ${durationPerTrial.toFixed(1)} ms`);
+  }
+}
+
+main().catch((err: unknown) => {
+  console.error(err);
+});