fix(GraphQL): fix internal Aliases name generation (#7009)

[abhimanyusinghgaur]

This PR modifies how the internal graph aliases are generated in case of multiple aliases of same field in the query.
For the given graphql query:

query {
      queryAuthor {
        name
        p1: posts(filter: {isPublished: true}){
          title
          text
        }
        p2: posts(filter: {isPublished: true}){
          title
          text
        }
      }
    }

earlier it was rewritten into:

query {
      queryAuthor(func: type(Author)) {
        name : Author.name
        posts : Author.posts @filter(eq(Post.isPublished, true)) {
          title : Post.title
          text : Post.text
          dgraph.uid : uid
        }
        posts1 : Author.posts @filter(eq(Post.isPublished, true)) {
          title : Post.title
          text : Post.text
          dgraph.uid : uid
        }
        dgraph.uid : uid
      }
    }

Now it is changed to:

query {
      queryAuthor(func: type(Author)) {
        name : Author.name
        posts : Author.posts @filter(eq(Post.isPublished, true)) {
          title : Post.title
          text : Post.text
          dgraph.uid : uid
        }
        posts.1 : Author.posts @filter(eq(Post.isPublished, true)) {
          title : Post.title
          text : Post.text
          dgraph.uid : uid
        }
        dgraph.uid : uid
      }
    }

(cherry picked from commit 953f656)

chore: fix a broken test (#7130)

The test broke after merging #7009 in master.

(cherry picked from commit 09274fb)

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