Fix prefer-to-have-count rule for expect arguments that need dereferencing

[An631]

ISSUE #293:
The current prefer-to-have-count rule has a problem where any expect checks that take a variable argument will not check to make sure the value is not originating from a .count call.

For example the following code would not be flagged as an error:

   const filesCount = await files.count();
   expect(filesCount).toBe(2);

The current code misses this case because we are not dereferencing the last assigned value of filesCount at the moment of verifying the expect argument. The rule should flag the error and return the following as a fix:

   const filesCount = files;
   await expect(filesCount).toHaveCount(2);

SOLUTION:

This PR updates the prefer-to-have-count code to re-use the dereference method previously used by the prefer-web-first-assertion rule. To make this method available to other files I moved it, along with all its related methods, to the ast.ts file which looked to me like the best place to centralize it (curious to know if there is a better place for these methods though).

I have added multiple new tests to check for other edge cases like variable re-assignment.

[github-actions]

🎉 This PR is included in version 1.6.2 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀