test(amazonq): performance test for building index and sending to LSP. (aws#5685)

## Problem
continuation of reliability work

## Solution
`buildIndex` in `src/amazonq/lsp/lspController.ts` captures many
potentially high risk paths in a single function, such as some I/O
operations and searching for project directories.

Thresholds determined by running in CI a few times and multiplying the
observed median by 1.5 to 2.0 depending on variance.

The "many files" test does 250 files w/ 10 bytes each. The "large files"
does 10 files w/ 1000 bytes each. These values were chosen to avoid
flakiness in CI.

Included in this PR is removing the use of fs-extra in
`src/amazonq/lsp/lspController.ts`

---

<!--- REMINDER: Ensure that your PR meets the guidelines in
CONTRIBUTING.md -->

License: I confirm that my contribution is made under the terms of the
Apache 2.0 license.

Author: Hweinstock

packages/core/src/testInteg/buildIndex.test.ts

@@ -0,0 +1,60 @@
+/*!
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import { performanceTest } from '../shared/performance/performance'
+import * as sinon from 'sinon'
+import * as vscode from 'vscode'
+import assert from 'assert'
+import { LspClient, LspController } from '../amazonq'
+import { LanguageClient, ServerOptions } from 'vscode-languageclient'
+import { createTestWorkspace } from '../test/testUtil'
+import { GetUsageRequestType, IndexRequestType } from '../amazonq/lsp/types'
+import { getRandomString } from '../shared'
+
+interface SetupResult {
+    clientReqStub: sinon.SinonStub
+}
+
+async function verifyResult(setup: SetupResult) {
+    assert.ok(setup.clientReqStub.calledTwice)
+    assert.ok(setup.clientReqStub.firstCall.calledWith(IndexRequestType))
+    assert.ok(setup.clientReqStub.secondCall.calledWith(GetUsageRequestType))
+}
+
+async function setupWithWorkspace(numFiles: number, options: { fileContent: string }): Promise<SetupResult> {
+    // Force VSCode to find my test workspace only to keep test contained and controlled.
+    const testWorksapce = await createTestWorkspace(numFiles, options)
+    sinon.stub(vscode.workspace, 'workspaceFolders').value([testWorksapce])
+    // Avoid sending real request to lsp.
+    const clientReqStub = sinon.stub(LanguageClient.prototype, 'sendRequest').resolves(true)
+    LspClient.instance.client = new LanguageClient('amazonq', 'test-client', {} as ServerOptions, {})
+    return { clientReqStub }
+}
+
+describe('buildIndex', function () {
+    describe('performanceTests', function () {
+        afterEach(function () {
+            sinon.restore()
+        })
+        performanceTest({}, 'indexing many small files', function () {
+            return {
+                setup: async () => setupWithWorkspace(250, { fileContent: '0123456789' }),
+                execute: async () => {
+                    await LspController.instance.buildIndex()
+                },
+                verify: verifyResult,
+            }
+        })
+        performanceTest({}, 'indexing few large files', function () {
+            return {
+                setup: async () => setupWithWorkspace(10, { fileContent: getRandomString(1000) }),
+                execute: async () => {
+                    await LspController.instance.buildIndex()
+                },
+                verify: verifyResult,
+            }
+        })
+    })
+})