Single-line imports are unnecessarily wrapped

Imports that could fit on a single line are unnecessarily wrapped:

/* 50 characters:
0        1         2         3         4         5
12345678901234567890123456789012345678901234567890
*/
use aaaaaaaaa::{bbbbbbbbb, ccccccccc, ddddddddd};

After rustfmt --config max_width=50:

/* 50 characters:
0        1         2         3         4         5
12345678901234567890123456789012345678901234567890
*/
use aaaaaaaaa::{
    bbbbbbbbb, ccccccccc, ddddddddd,
};

The use declaration is only 49 characters but gets wrapped anyway. This also happens with the default max_width of 100 (use declarations > 98 characters get wrapped).

Reproduce the behavior in rustfmt with the example use declaration and --config max_width=50, then inspect the formatting path for use declarations. Compare the measured width with the wrapping decision and add coverage for declarations that fit exactly within the configured width. Done means eligible single-line imports remain on one line without changing imports that exceed the limit.