Support generic bounds on implement macro

[roblabla]

Suggestion

Currently, the implement macro does not support generic bounds. For instance, the following:

trait MyClass {}

#[implement(IClassFactory)]
struct MyClassFactory<T>(PhantomData<T>);

impl<T: MyClass> IClassFactory_Impl for MyClassFactory<T> {
    // ...
}

Will fail to compile with the following error:

error[E0277]: the trait bound `T: MyClass` is not satisfied
    --> src/lib.rs:185:1
     |
185  | #[implement(IClassFactory)]
     | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MyClass` is not implemented for `T`, which is required by `MyClassFactory<T>: IClassFactory_Impl`
     |
note: required for `MyClassFactory<T>` to implement `IClassFactory_Impl`
    --> src/lib.rs:188:23
     |
188  | impl<T: MyClass> IClassFactory_Impl for MyClassFactory<T> {
     |         -------  ^^^^^^^^^^^^^^^^^^     ^^^^^^^^^^^^^^^^^
     |         |
     |         unsatisfied trait bound introduced here
note: required by a bound in `IClassFactory_Vtbl::new`
    --> /Users/roblabla/.cargo_isengard/registry/src/index.crates.io-6f17d22bba15001f/windows-0.52.0/src/Windows/Win32/System/Com/impl.rs:1191:81
     |
1191 |     pub const fn new<Identity: ::windows_core::IUnknownImpl<Impl = Impl>, Impl: IClassFactory_Impl, const OFFSET: isize>() -> IClassFactory_Vtbl {
     |                                                                                 ^^^^^^^^^^^^^^^^^^ required by this bound in `IClassFactory_Vtbl::new`
     = note: this error originates in the attribute macro `implement` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider restricting type parameter `T`
     |
186  | struct MyClassFactory<T: MyClassProvider>(PhantomData<T>);
     |                          ++++++++++++++

Doing the suggested change (adding the bound on the struct) doesn't help:

error[E0107]: struct takes 1 generic argument but 0 generic arguments were supplied
   --> src/lib.rs:186:8
    |
186 | struct MyClassFactory<T: MyClass>(PhantomData<T>);
    |        ^^^^^^^^^^^^^^^^ expected 1 generic argument
    |
note: struct defined here, with 1 generic parameter: `T`
   --> src/lib.rs:186:8
    |
186 | struct MyClassFactory<T: MyClass>(PhantomData<T>);
    |        ^^^^^^^^^^^^^^^^ -
help: add missing generic argument
    |
185 | #T, [implement(IClassFactory)]
    |  ++

IMO, if a generic bound is found on the struct that implements is on, it should use it for all the generated impl block.

---

My use-case is to provide a safe wrapper around a COM interface. I'm creating a trait that mirrors the COM interface's trait, but wrapping all the structures in safe wrappers, to hopefully make implementing it easier and safer.

[kennykerr]

Keep in mind that the generic support provided by the implement macro is intended to handle WinRT generic interfaces, but I'm certainly happy to expand it to support generic programming in general so I welcome the improvement.