fix(DQL): ignore ordering of indexes in schema with eq function

[OmarAyo]

Previously, the following schema:

name: string @index(trigram, term) .
with some added data, and the following query:

query {
q(func: eq(name, "Alice", "Bob")) {
uid
name
}
}
would error out saying it doesn't have a valid tokenizer:

{
"errors": [
{
"message": ": Attribute name does not have a valid tokenizer.",
"extensions": {
"code": "ErrorInvalidRequest"
}
}
],
"data": null
}
even though term index is present on the predicate.
On the other hand, if you reversed the order of indexes:

name: string @index(term, trigram) .
It would give correct results:

{
"data": {
"q": [
{
"uid": "0x2",
"name": "Alice",
"age": 20
},
{
"uid": "0x3",
"name": "Bob",
"age": 25
}
]
}
}
This PR fixes the above issue.

(cherry picked from commit 0b11439)

---

This change is 

[danielmai]

Reviewable status: 0 of 3 files reviewed, all discussions resolved (waiting on @danielmai, @manishrjain, and @MichaelJCompton)