Don't merge crates when `imports_granularity="Module"`

[mnkhouri]

When merging imports using imports_granularity="Module", individual crate imports should get their own use statement on a new line.

// Before this commit:
use {library1, library2 as lib2, library3};

// After this commit:
use library1;
use library2 as lib2;
use library3;

Fixes: #6191