* Disable `complex` when compiling for Windows

Libffi does not include any code for complex types when `_WIN32` is
defined.

* Fix padding on structs in `libffi-sys`

* `ffi_raw` and `ffi_trampoline` does not have an explicit padding set
  by libffi.
* `ffi_closure` is padded to 8 bytes and has an extra padding field when
  compiling with MSVC for i686.

* Set the correct ABI for x86_64 MSVC

The default ABI when compiling for x86_64 with MSVC was set to GNUW64
instead of the expected WIN64. This caused an error when passing
`double`s to and from functions.

* Fixed warning about unused import on Windows

`std::path::{Path, PathBuf}` was imported in the build scripts of
libffi-sys, but not used on Windows. This moves the import to
`not_msvc.rs` to avoid the error message.

* Clean up and modify build script for msvc

* Use the full (relative) path for all files and folders to
  keep every file and folder path consistent.
* Use separate header files for x86, x86_64, and aarch64. See the bottom
  of the commit message for the commands used to generate the headers.
* Use compiler from `cc` crate instead of looking for `cl.exe` using
  `cc::windows_registry`. This will hopefully open up for
  cross-compiling for msvc targets in the future.
* Store the resulting assembly file from pre-processing in the target
  directory instead of inside `libffi-sys-rs/libffi/`.
* Define `FFI_STATIC_BUILD` when building for MSVC.
* Emit helpers for cargo for when to recompile libffi.

The headers were generated using Visual Studio 2022 and
msys2-x86_64-20250221.

The headers for x86_64 were generated using the following command:
`./configure --build x86_64-pc-msys --target x86_64-pc-msys --host x86_64-pc-msys --disable-dependency-tracking --with-pic --disable-shared --disable-docs CC="$(pwd)/msvcc.sh -m64" CXX="$(pwd)/msvcc.sh -m64" CPP="cl.exe -nologo -EP" CXXCPP="cl.exe -nologo -EP"`

The headers for i686 were generated using the following command:
`./configure --build i686-pc-msys --target i686-pc-msys --host i686-pc-msys --disable-dependency-tracking --with-pic --disable-shared --disable-docs CC="$(pwd)/msvcc.sh" CXX="$(pwd)/msvcc.sh" CPP="cl.exe -nologo -EP" CXXCPP="cl.exe -nologo -EP"`

The headers for aarch64 were generated using the following command:
`./configure --build x86_64-pc-msys --target aarch64-pc-msys --host aarch64-pc-msys --disable-dependency-tracking --with-pic --disable-shared --disable-docs CC="$(pwd)/msvcc.sh -m64" CXX="$(pwd)/msvcc.sh -m64" CPP="cl.exe -nologo -EP" CXXCPP="cl.exe -nologo -EP"`

* Select build process by `CARGO_CFG_TARGET_ENV`

`target_env` represent the host building the code for build scripts, and
does not necessarily reflect the target platform. This change uses
`CARGO_CFG_TARGET_ENV` to select the correct build process.

Currently, it is seemingly not possible to cross-compile libffi-sys for
MSVC, but it might be possible in the future.

Type tags are stored in the `type_` field of `ffi_type`s, which is a
`c_ushort`. `c_ushort` is an unsigned integer with at least 16 bits. On
most modern architectures, `c_ushort` is equivalent to `u16`.

This commit changes the types of the constants used for the `type_`
field to `u16` to avoid having to cast the constants when using them.

Removes duplicate definitions of the following symbols:

* libffi_sys::ffi_type_complex_longdouble
* libffi::middle::types::longdouble
* libffi::middle::types::complex_longdouble
* libffi::middle::Type::complex_longdouble

Added `ffi_type`s to `middle::types` that can be used when testing
`middle::Type` with miri.

This adds another test to `middle::types` that tests the behavior when
cloning and dropping `Type`s. The test can run with miri.

`longdouble` does not work with "system" feature on MacOS.