Auto merge of #100004 - jyn514:exclude-single-test, r=Mark-Simulacrum

Move `x test --skip` to be part of `--exclude`

`--skip` is inconsistent with the rest of the interface and redundant with `--exclude`.
Fix --exclude to work properly for files and directories rather than having a separate flag.

Fixes rust-lang/rust#96342. cc rust-lang/rust#96493 (comment)

r? `@Mark-Simulacrum`

Author: bors