Fix duplicate input measures error

[WilliamDee]

Resolves #969

Description

Currently, when running through the branch combiner, in an instance where you have 2 derived metrics that contains the same input measure, it would get combined and it doesn't get deduped. Example,

metric:
  name: "derived1"
  description: Test child derived metric 1
  type: derived
  type_params:
    expr: "booking_value + bookings"
    metrics:
      - name: booking_value
      - name: bookings
---
metric:
  name: "derived2"
  description: Test child derived metric 2
  type: derived
  type_params:
    expr: "bookings + instant_bookings"
    metrics:
      - name: instant_bookings
      - name: bookings
---
metric:
  name: "derived_parent"
  description: Test parent derived metric
  type: derived
  type_params:
    expr: "derived1 + derived2"
    metrics:
      - name: derived1
      - name: derived2

This leads to hitting an error during the dataflow rendering where we matched 2 duplicate input measures when expecting only 1 (here). Additionally, the parser in dbt-core utilizes it's own rewritten set of transformation rules and it currently isn't doing any deduping, this is a bug and should be fixed within dbt-core, tho it isn't affecting this issue.

NOTE: this error only occurs from manifests parsed by dbt-core, which is why the error never popped up in MF as MF uses the transformation rules in DSI.

1. Dedupe the combined input measure specs
2. Dedupe metric input measures in transformation rule (to remove after change is in core)

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