Fix of Slicer image not good #4992

Tighter parsing of PrusaSlicer's own G-code annotations
to avoid clashes with comments inside user G-codes.

Also the GCodeReader was extended to return string_views instead
of copying a substring, and the GCodeProcessor was partially adapted
to string_views.

src/libslic3r/ExtrusionEntity.cpp

@@ -331,7 +331,7 @@ std::string ExtrusionEntity::role_to_string(ExtrusionRole role)
     return "";
 }
 
-ExtrusionRole ExtrusionEntity::string_to_role(const std::string& role)
+ExtrusionRole ExtrusionEntity::string_to_role(const std::string_view role)
 {
     if (role == L("Perimeter"))
         return erPerimeter;