[BUGFIX beta] Align Em.isArray behavior with Array.isArray for FileList type

[kamilogorek]

FileList type is currently detected as array, however it doesn't provide it's methods like forEach or map.
Also Array.isArray doesn't consider FileType as an array.

This PR unifies this behavior and fixes #12688.

[kamilogorek]

It appears that IE9 test is failing because of FileList API absence.

[stefanpenner]

If you are looking for an array, is there a reason to not use Array.isArray? What scenario lead you to discover this quirk?

We need to be careful that his doesn't have unexpected side affects, are there scenarios were the current check results in behavior someone legitimately relies on? What other cases are missing. Is this form of type checking actually flawed?

[kamilogorek]

@stefanpenner CCing @joelcox from this issue, as he is the one who found this culprit #12688

[joelcox]

Thanks for working on this fix @kamilogorek. I encountered this behavior while working on an internal file upload component (based on ember-uploader), which was set up in such a way that it would accept both an array of files, or a single file.

[homu]

☔ The latest upstream changes (presumably #13658) made this pull request unmergeable. Please resolve the merge conflicts.

[mixonic]

@kamilogorek can you just move the fileList assertions into a separate test that only runs if fileList support is present? That would seem sufficient.

[kamilogorek]

Sure, will do! I'll update PR within 24h when I get home.
Ok, maybe a little longer as I don't have an access to my laptop before Monday, sorry...

[kamilogorek]

@mixonic like this?

[mixonic]

Yeah this looks great to me @kamilogorek. r+ @rwjblue?

[homu]

☔ The latest upstream changes (presumably #14215) made this pull request unmergeable. Please resolve the merge conflicts.

[kamilogorek]

Resolved.

[rwjblue]

Thanks @kamilogorek!