refactor: clear client caches on stop request (#1374)
refactor: clear client caches on stop request (#1374)

The command to restart the language server calls `client.stop` followed
by `client.start`. We should clear the caches so that the restart
command starts with a clean state.
angular/vscode-ng-language-service,angular/vscode-ng-language-service,angular/vscode-ng-language-service,angular/vscode-ng-language-service