fix(telemetry): session_end not caching events (#5817)

## Problem

When the user shutdown their extension gracefully our mechanism that
would cache any pending metrics for the next startup would not save to
disk.

This was due to the VS Code FS implementation being used, but it will
not work since the function it is called in is called by `deactivate()`
which does not have access to vscode apis on shutdown.

## Solution

Solution is to swap it with the node fs implementation
---

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

Signed-off-by: nkomonen-amazon <[email protected]>

packages/core/src/shared/telemetry/telemetryService.ts

@@ -20,6 +20,7 @@ import { ClassToInterfaceType } from '../utilities/tsUtils'
 import { getClientId, validateMetricEvent } from './util'
 import { telemetry, MetricBase } from './telemetry'
 import fs from '../fs/fs'
+import fsNode from 'fs/promises'
 import * as collectionUtil from '../utilities/collectionUtils'
 
 export type TelemetryService = ClassToInterfaceType<DefaultTelemetryService>
@@ -116,7 +117,10 @@ export class DefaultTelemetryService {
             })
 
             try {
-                await fs.writeFile(this.persistFilePath, JSON.stringify(this._eventQueue))
+                /**
+                 * This function runs in deactivate() so we must use node fs. See the vscode behavior doc for more info.
+                 */
+                await fsNode.writeFile(this.persistFilePath, JSON.stringify(this._eventQueue))
             } catch {}
         }
     }