json.wrap tracked WrapDB's legacy json package, which has been frozen at
3.2.0-1 since upstream renamed it. It also carried no wrapdb_version field, so
`meson wrap update` could not tell what it was upgrading from and the bump
script skipped it silently, leaving us stuck on a 2018 release.
Point the wrap at nlohmann/json directly rather than routing through WrapDB,
which is slow to adopt upstream releases. Upstream has shipped a root
meson.build declaring nlohmann_json_dep since 2017, so no packaging overlay is
needed and ui/thirdparty keeps asking for the same dependency name.
The revision stays on v3.2.0 so this is only a change of mechanism. The bump
script can now carry it forward to v3.12.0 on its own.
Matt Borgerson
6ccd229c74