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.

先找出 GraphQLResolveInfo 和 GraphQLFieldResolver 的 Python 定義與使用位置，接著將它們處理 context 的方式與 issue 中的 GraphQL.js 範例進行比較。完成的標準是，使用者可以提供 context 型別，而 GraphQLResolveInfo 不會將其視為 Any；請根據專案現有的型別標註與 resolver 覆蓋情況驗證這項變更。