Implement fix for Fast Refresh bug

[JonnyBurger]

Fixes the bug described in #228.

Verified by checking that the example posted in the original issue works now, null is not returned, and by adding a test that failed before the fix.

[JonnyBurger]

Just noticed that a test is failing and am a bit lost on how this could be correctly fixed..

There is a test that asserts that getTimeInfoEntries should not have files with invalid names in their map. However Webpack relies on it here:

https://github.com/webpack/webpack/blob/4b4ca3bb53f36a5b8fc6bc1bd976ed7af161bd80/lib/FileSystemInfo.js#L2102-L2105

In this code snippet, getting the file timestamps for a file with wrong casing returns null, which is neither undefined nor ignore and therefore the module does not get invalidated.
Maybe this should be fixed on Webpack side instead?

Need some help in figuring out what the right way to approach it is, until then I need to pause on this issue.

[alexander-akait]

I don't think it is the valid fix, some OS has case-insensitive logic, same case-sensivity, it should be under an option (or we should check it using node.js API, not sure we can check it). Why your files have different cases, it is a not good practice (even more - there are plugins and rules for linter to prevent such things). But I agree it should be considered as a bug