meson: Always look for both cmake and pkgconfig names

meson: Always look for both cmake and pkgconfig names

The is_msvc_like change is wrong; it used a false correlation between
"compiler being used" and "dependency method" by saying that on
Windows, when building with MSVC, you will only use CMake to find png,
jpeg, tiff.

You can use pkgconfig to find these deps on Windows with MSVC -- when
the deps have been built with Autotools or Meson (with MSVC). You can
also find these deps using CMake on other platforms like macOS or
Linux.

The solution is simple: just search for both names on all platforms,
and just search for the pkgconfig name first.