"[provides]" section cannot be omitted in wrap files

The [wrapdb documentation](https://mesonbuild.com/Wrap-dependency-system-manual.html#provide-section) states that (since meson ???)

> A wrap file named `foo.wrap` implicitly provides the dependency name foo even when the `[provide]` section is missing.

But this is not accounted for in `sanity_checks.py` as far as I can see.

Start by reading the wrapdb documentation section linked in the issue and inspect sanity_checks.py to find how missing [provide] sections are handled. Confirm the expected behavior for a wrap file named foo.wrap, then check the surrounding validation logic and any relevant tests. Done means the documented omission is accepted by sanity checks.

Written by the indexing model from the issue text.