Closes https://github.com/neovim/neovim/issues/15063

Allows using Neovim core functions using LuaJIT FFI on Windows.

Do not copy a lot of lua strings (dict keys) to just strequal() them
Just compare them directly to a dedicated hash function.

feat(generators): HASHY McHASHFACE

PVS erroneously flags our DEFINE_FUNC_ATTRIBUTES guard:

  V1049 The 'DEFINE_FUNC_ATTRIBUTES' include guard is already defined in
  the 'lang.h.generated.h' header. The 'profile.h.generated.h' header
  will be excluded from compilation.

To satisfy PVS, just remove the `#ifndef` check. It's not needed anyway:
C allows to redundantly #define a macro.

https://gcc.gnu.org/onlinedocs/cpp/Undefining-and-Redefining-Macros.html

> if an identifier which is currently a macro is redefined, then the new
> definition must be effectively the same as the old one
> ...
> If a macro is redefined with a definition that is not effectively the
> same as the old one, the preprocessor issues a warning and changes the
> macro to use the new definition. If the new definition is effectively
> the same, the redefinition is silently ignored. This allows, for
> instance, two different headers to define a common macro. The
> preprocessor will only complain if the definitions do not match.

Preprocessor directives on the first line of the file were not being parsed.