Also removes a bunch of std::string stuff from the file handling in the
simulator. All our file handling, env variable expansion, project path,
etc. stuff is wxString based, and jumping through std::string in between
just makes it more complex and increases the potential bug surface.
Also fixes a bug where you'd get two error messages when a spice model
library wasn't found.
Also fixes a bug where you'd get a spice model library not found error
when the text field was empty.
Also fixes a bug where we'd try to absolutize a path starting with an
unresolved text or environment variable. If the path starts with a
variable it's probably absolute, and tacking on the project path in the
error message just obfuscates things.
Fixes https://gitlab.com/kicad/code/kicad/issues/13082
b15913bd53