Returns or sets the file path of the shader code to execute as a String (for example,
"\Application\bin\nt-x86-64\sibase.dll" or "{LIBS}/sibase.{EXT}". This is the same information
as specified in the FileName entry under the MetaShader > Renderer section in a SPDL file.
If the file path hasn't been set then an empty string is returned.
