`find_package(CURL CONFIG)` provides `CURL_VERSION` from the upstream
cmake package version file.
Upstream curl commit `699ac9430c` (cmake: publish/check supported
protocols/features via `CURLConfig.cmake`, 2024-12-29) extends the
upstream cmake package to provide our old `CURL_VERSION_STRING`.
Provide both names from CMake's own module to aid transition.
Fixes: #26634
Upstream CURL provides imported target `CURL::libcurl`. Rename the
target added by `FindCURL` to match. We don't need compatibility with
the old name because it has never been in a CMake release (except a 3.12
release candidate).
Suggested-by: Jakub Zakrzewski <slither.jz@gmail.com>
Acked-by: Rolf Eike Beer <eike@sf-mail.de>
Fixes: #18091
