Fix faulty import

During the build process, we now get errors pointing out that we import two different
items and call them `QueryServerClient`. One is actually the legacy one and has been
superseded by the new one so far.

Let's fix this and appease the linter.

Full errors:

```

[gulp-typescript]
/home/runner/work/vscode-codeql/vscode-codeql/extensions/ql-vscode/src/extension.ts(88,9):
error TS2300: Duplicate identifier 'QueryServerClient'.

[gulp-typescript]
/home/runner/work/vscode-codeql/vscode-codeql/extensions/ql-vscode/src/extension.ts(89,9):
error TS2300: Duplicate identifier 'QueryServerClient'.

[gulp-typescript]
/home/runner/work/vscode-codeql/vscode-codeql/extensions/ql-vscode/src/extension.ts(1596,30):
error TS2345: Argument of type
'import("/home/runner/work/vscode-codeql/vscode-codeql/extensions/ql-vscode/src/legacy-query-server/queryserver-client").QueryServerClient'
is not assignable to parameter of type
'import("/home/runner/work/vscode-codeql/vscode-codeql/extensions/ql-vscode/src/query-server/queryserver-client").QueryServerClient'.

```

Author: elenatanasoiu

extensions/ql-vscode/src/extension.ts

@@ -85,7 +85,7 @@ import {
 } from "./common";
 import { QueryHistoryManager } from "./query-history";
 import { CompletedLocalQueryInfo, LocalQueryInfo } from "./query-results";
-import { QueryServerClient } from "./legacy-query-server/queryserver-client";
+import { QueryServerClient as LegacyQueryServerClient } from "./legacy-query-server/queryserver-client";
 import { QueryServerClient } from "./query-server/queryserver-client";
 import { displayQuickQuery } from "./quick-query";
 import { QLTestAdapterFactory } from "./test-adapter";
@@ -1604,7 +1604,7 @@ async function createQueryServer(
     await qs.startQueryServer();
     return new NewQueryRunner(qs);
   } else {
-    const qs = new QueryServerClient(
+    const qs = new LegacyQueryServerClient(
       qlConfigurationListener,
       cliServer,
       qsOpts,