Implement `derive_provider` macros

[soareschen]

Summary

The derive_provider macros would allow trait-generic providers to be automatically implemented following similar boilerplates. Below are some examples:

WithProvider

#[derive_provider(WithProvider)]
#[cgp_component { name: NameTypeComponent, provider: ProvideNameType }]
pub trait HasNameType {
  type Name;
}

would have the following derived:

impl<Context, Provider, Type> ProvideNameType<Context> for WithProvider<Provider>
where
  Provider: ProvideType<NameTypeComponent, Type = Name>,
{
  type Name = Name;
}

UseContext

#[derive_provider(UseContext)]
#[cgp_component { provider: NameGetter }]
pub trait HasName {
  fn get_name(&self) -> &String;
}

would have the following derived:

impl<Context> NameGetter<Context> for UseContext
where
  Context: HasName,
{
  fn get_name(context: &Context) -> &String {
    context.get_name()
  }
}

UseField

#[derive_provider(UseField)]
#[cgp_component { provider: NameGetter }]
pub trait HasName {
  fn get_name(&self) -> &String;
}

Would have the following derived:

impl<Context, Tag> NameGetter<Context> for UseField<Tag>
where
  Context: HasField<Tag, Value = String>,
{
  fn get_name(context: &Context) -> &String {
    context.get_field(PhantomData)
  }
}