Add the ability to specify `GraphQLResolveInfo.context` type

Currently, `GraphQLResolveInfo.context` is being typed as `Any`, making `GraphQLResolveInfo` a generic would give users the ability to provide their type. This is already being done in `GraphQL.js`
```
export type GraphQLFieldResolver<
TSource,
TContext,
TArgs = any,
TResult = unknown,
> = (
source: TSource,
args: TArgs,
context: TContext,
info: GraphQLResolveInfo,
) => TResult;
```

If this change will be welcome, I'd like to make a pull-request implementing it.