Fix pkg-config files being broken on MSVC-built static libraries

[Cacodemon345]

When libjxl is built as a static library with MSVC, the pkg-config files are not configured properly to account for statically-built library names, causing link failures.

This PR makes those files account for statically-built libraries that are built by MSVC.

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[HappySeaFox]

I propose to rename jxl-static back to jxl on all platforms. This will simplify searching for libjxl in CMake with find_library and possibly other non-pkg-config environments.

[kmilos]

I propose to rename jxl-static back to jxl on all platforms. This will simplify searching for libjxl in CMake with find_library and possibly other non-pkg-config environments.

Sadly does not work well for MSVC builds where the shared import library and static one cannot coexist with the same base name.

[HappySeaFox]

Sadly does not work well for MSVC builds where the shared import library and static one cannot coexist with the same base name.

This is a build system-related problem. One of the possible solutions could be putting shared and static libs into different folders.

Another possible solution is to provide CMake configs so find_package(jxl) always finds the correct library. I would vote for this solution even more than for the renaming.

P.S. I can name just a couple of libs I'm aware of that have different names for shared and static versions. It's always pain for a build system to deal with such libs as they frequently don't provide CMake configs and need runtime patching.

UPDATE #2851