Auto merge of #114750 - Enselic:metadata-dep-info, r=compiler-errors

Make `.rmeta` file in `dep-info` have correct name (`lib` prefix)

Since `filename_for_metadata()` and
`OutputFilenames::path(OutputType::Metadata)` had different logic for the name of the metadata file, the `.d` file contained a file name different from the actual name used. Share the logic to fix the out-of-sync name.

Without this fix, the `.d` file contained

    dash-separated_something-extra.rmeta: dash-separated.rs

instead of

    libdash_separated_something-extra.rmeta: dash-separated.rs

which is the name of the file that is actually written by the compiler.

Worth noting: It took me several iterations to get all tests to pass, so I am relatively confident that this PR does not break anything.

Closes #68839

Author: bors