Describe the bug
The cmake wrapper for wxWidgets expects libpng to always be called png.lib but it is not on static triplets so it fails to find the library to link when you try to use wxWidgets.

Environment

• OS: Windows
• Compiler: cl.exe 19.28.29910

To Reproduce
Steps to reproduce the behavior:

1. ./vcpkg install wxwidgets:x64-windows-static
2. Try to use wxWidgets from your own statically linked project via CMake

Expected behavior
Successful linking

Failure logs
fatal error LNK1104: cannot open file 'png.lib'

Additional context
libpng's library for static triplets is called png_static so using png won't work.

I have a pull request ready that I will add after filing this issue.