refactor: remove Session.getDefaultLanguageService()
refactor: remove Session.getDefaultLanguageService()

The method above could be merged with `Session.getLSAndScriptInfo()`,
so we don't need to have so many layers of indirection.

angular/vscode-ng-language-service,angular/vscode-ng-language-service,angular/vscode-ng-language-service,angular/vscode-ng-language-service