Rollup merge of #137020 - ferrocene:pa-vendor-sources, r=Kobzol

Pass vendored sources from bootstrap to generate-copyright

In addition to doing the vendoring in bootstrap, this PR also loads the list of manifests to parse from bootstrap (instead of hardcoding a smaller list in generate-copyright). This is best reviewed commit-by-commit.

Fixes rust-lang/rust#136955

Author: matthiaskrgr