Fix unexpected behaviour for @wordpress/is-shallow-equal package.

[nerrad]

Describe the bug
The docs for this package describe being able to import two specific exports for is-shallow-equal:

You can import a specific implementation if you already know the types of values you are working with:

import isShallowEqualArrays from '@wordpress/is-shallow-equal/arrays';
import isShallowEqualObjects from '@wordpress/is-shallow-equal/objects';

However, with the latest release of the package this no longer works. When building using webpack, the build fails with:

ERROR in ./src/index.js
Module not found: Error: Can't resolve '@wordpress/is-shallow-equal/arrays'

To Reproduce
I've created a repository with some simple code to demonstrate what happens.

[aduth]

The root cause of this is that the require semantics were expecting arrays.js and objects.js files in the root module directory. These no longer exist (they live in build), as apparently the package is now subject to the transpile build step (it was not originally).

[aduth]

See #7556 , cc @gziolo @omarreiss