fix syntax error at #[derive(Props)] using const generics

[syrflover]

Reproduce problem

https://github.com/syrflover/derive-props-with-const-generics

To trigger an error, change the version of dioxus to 0.4 in Cargo.toml

What is problem

dioxus/packages/core-macro/src/props/mod.rs

Lines 554 to 566 in a3e6d0a

	let phantom_generics = self.generics.params.iter().map(|param| match param {
	syn::GenericParam::Lifetime(lifetime) => {
	let lifetime = &lifetime.lifetime;
	quote!(::core::marker::PhantomData<&#lifetime ()>)
	}
	syn::GenericParam::Type(ty) => {
	let ty = &ty.ident;
	quote!(::core::marker::PhantomData<#ty>)
	}
	syn::GenericParam::Const(_cnst) => {
	quote!()
	}
	});

dioxus/packages/core-macro/src/props/mod.rs

Lines 645 to 651 in a3e6d0a

	#[must_use]
	#builder_type_doc
	#[allow(dead_code, non_camel_case_types, non_snake_case)]
	#vis struct #builder_name #b_generics {
	fields: #all_fields_param,
	_phantom: (#( #phantom_generics ),*),
	}

When it is GenericParam::Const, it doesn't return anything. However, if that item is included in an iterator, a syntax error occurs because it generates commas as many times as the length of the iterator when creating tokens.

How to fixed it

https://github.com/syrflover/dioxus/blob/4f8b60834af43fef879c7eb0ff46b74d23a6eabe/packages/core-macro/src/props/mod.rs#L554-L564

Changed to returns None, when it is GenericParam::Const using filter_map.

[ealmloff]

Good catch and very clear explanation, thank you!