fix(babel): support for dynamic keys in objects with css as values

[Anber]

Motivation

Support for syntax like that:

import { css } from '@linaria/core';
import { TestEnum } from './ts-data.ts';

export const object = {
	[TestEnum.FirstValue]: css``,
	[TestEnum.SecondValue]: css``,
}

Summary

For now, Linaria throws an error if meets a dynamic key. After this PR, Linaria will use normalized source code between [] as a display name for the generated class.

Test plan

New test was added.