Safe replacement of a lot of `!count()` with `=== []`

Safe replacement of a lot of `!count()` with `=== []`

This was originally a global search and replace. I manually checked all
replacements and reverted them if (due to the lack of type hints) either
null (that would be 0 when counted) or a Countable object can end in the
variable or property in question.

Now this patch only touches places where I'm sure nothing can break.

For the sanity of the honorable reviewers this patch is exclusively touching
negated counts. You should not find a single `!== []` in this patch, that
would be a mistake.

Change-Id: I5eafd4d8fccdb53a668be8e6f25a566f9c3a0a95