Fix: [Script] Improve ScriptText validation (#11721)

The validation is now done in two steps:
- First we get the list of parameters in the same order they used to be in encoded string
- Then we validate the parameter types like FormatString would use them while encoding the string

Codechange: use std::string without const as return

Otherwise some compilers, e.g. MSVC, do not pick up that these are temporaries
and as such it will pass the temporaries to `const std::string &` instead of
the wanted `std::string &&`

Codechange: Use override specifer for overriding member declarations

This is a C++11 feature that allows the compiler to check that a virtual
member declaration overrides a base-class member with the same signature.

Also src/blitter/32bpp_anim_sse4.hpp +38 is no longer erroneously marked
as virtual despite being a template.