windows-bindgen generated _Impl trait methods can be simplified

[omerkattan-microsoft]

Suggestion

A COM interface whose methods are SAL annotated is usually simplified. However, the generated _Impl trait is less simplified.
For example, consider the following interface:

DEFINE_INTERFACE(ITestInterface, "7E17AD3C-47AF-4A71-85BD-1122EAB7E794") : public IUnknown
{
    STDMETHOD_(HRESULT, EncryptBuffer)
    (__in_bcount(cbSize) BYTE * pBuffer, _In_ size_t cbSize, _Out_ IBuffer * *ppvObj) = 0;
};

The generated ITestInterface looks like that:

impl ITestInterface {
    pub unsafe fn EncryptBuffer(
        &self,
        pbuffer: &mut [u8],
        ) -> windows_core::Result<IBuffer> {
        // ...
    }
}

pBuffer and cbSize were nicely merged into a mutable slice thanks to the SAL annotations. However, when implementing this interface we need to implement the following trait:

pub trait ITestInterface_Impl: Sized {
    fn EncryptBuffer(
        &self,
        pbuffer: *mut u8,
        cbsize: usize,
    ) -> windows_core::Result<IBuffer>;
}

The return value for the _Impl trait method was simplified, but not the slice param. If it was simplified as well, it would allow us to implement the interface without using unsafe code