feat: Extend lint-file to show which REUSE tags apply to the linted file(s)

[silverhook]

Currently, reuse lint-file only checks if the file is covered by some REUSE tags. Which is a great feature!

What would be even better though is if it could output which REUSE tags (and ideally where they came from) apply to the file.

Use case:

• massive code base with many un-commentable files
• I use one glob in REUSE.toml for all *.txt files to say these files are under CC0-1.0
• but use another glob in REUSE.toml (let’s keep it simple) for all docs/**/*.txt to say those specifically are under CC-BY-SA-4.0

Another use case:

• I am trying to check how the cardinality setting in REUSE.toml affects the output.

In both cases I want to know which license (and copyright holder) the file docs/bla/toot.txt is under.

Relevant:
#1055
#1068

---

More time- and resource-intense workaround (faster with rg, but works with grep too):

reuse spdx > tmp_reuse.spdx
rg "docs/bla/toot.txt" tmp_reuse.spdx --after-context=6 --before-context=1