src/vs/editor/common/services/languageService.ts/LanguageSelection/_evaluate
class LanguageSelection:	private _evaluate(): void {
		const languageId = this._selector();
		if (languageId === this.languageId) {
			// no change
			return;
		}
		this.languageId = languageId;
		this._emitter?.fire(this.languageId);
	}