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

Change: include fmt.h C++ headers in stdafx.h

This to prevent compilation issues between runs with and without precompiled
headers. Also remove the headers from the rest of the code base as they are
not needed there anymore, although they do relatively little harm.

Codechange: add non-nullptr asserts in cases where it should never be nullptr

Though where similar calls are checked for nullptr as in those instances of
the use of that function it can actually return nullptr. In other words, write
down the assumption that the function never returns nullptr in an assert.

Fix: Don't crash if reading a GS string file from disk produces an error.

The raw_strings vector may not include NULLs as no consumer can deal with it.

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.