Fixes #3282

The fix itself is contained in the using_directives bump to 1.1.2:

• https://github.com/VirtusLab/using_directives/releases/tag/v1.1.2

Specifically, it's this change:

• improvement: Accept coma only if followed by whitespace using_directives#61

What this PR does:

• bumps using_directives to 1.1.2
• adds tests ensuring the old syntax is no older honored (no longer can use commas on their own as value separators)
• adds tests for the deprecation of using commas with whitespace as value separators
• updates the syntax in docs, old code & tests (which contributes the most to the change line count)