feat(DQL): @groupby on scalar fields and count duplicate (#7746)

[MichelDiz]

PS. This PR depends A LOT in the Roaring Bitmaps. ref: 1134839

This PR extends support for var inside the @groupby query on a scalar predicate at root.
for example the given query now doesn't result to error:-

var(func: ... ) @groupby(age) {
  c as count(uid)
}

Now the uid variable c contains map of uid to count of uids with the same age.
Suppose for the data :-

        "uid": "0x1",
        "age": 38
      },
      {
        "uid": "0x17",
        "age": 15
      },
      {
        "uid": "0x18",
        "age": 15
      },
      {
        "uid": "0x19",
        "age": 17
      }

The following groupby query:-

var(func: uid(1, 23, 24, 25)) @groupby(age) {
      c as count(uid)
}
 me(func: uid(c)) {
      uid
      val(c)
}

returns the result:-

"data": {
    "me": [
      {
        "uid": "0x1",
        "val(c)": 1
      },
      {
        "uid": "0x17",
        "val(c)": 2
      },
      {
        "uid": "0x18",
        "val(c)": 2
      },
      {
        "uid": "0x19",
        "val(c)": 1
      }
    ]
  }

The behaviour will be the same if there are multiple predicates and some of them are uid predicates.
However, it is only supported at root currently. Hence the given query will still return error:-

var(func: .....) {
   friend @groupby(age) {
       a as count(uid)
   }
}

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[skrdgraph]

@MichelDiz - this is failing the build phase of the test. I would suggest you to make this a draft PR - and test things locally before opening it up for review.

[MichelDiz]

Closing, Follow this issue #8538