src/vs/platform/contextkey/common/contextkey.ts/ContextKeyAndExpr/negate
class ContextKeyAndExpr:	public negate(): ContextKeyExpression {
		if (!this.negated) {
			const result: ContextKeyExpression[] = [];
			for (const expr of this.expr) {
				result.push(expr.negate());
			}
			this.negated = ContextKeyOrExpr.create(result, this, true)!;
		}
		return this.negated;
	}