chore: move Northcott from NumberTheory.Height to Order (leanprover-community#39215)

Since the current module Mathlib.NumberTheory.Height.Northcott contains material that is not specific to heights (or number theory). we move it to Mathlib.Order.Northcott. This allows us to re-use the old module location to add a height-specific Northcott instance in a follow-up PR.

Author: MichaelStollBayreuth

Mathlib.lean

@@ -5635,7 +5635,6 @@ public import Mathlib.NumberTheory.Harmonic.Int
 public import Mathlib.NumberTheory.Harmonic.ZetaAsymp
 public import Mathlib.NumberTheory.Height.Basic
 public import Mathlib.NumberTheory.Height.MvPolynomial
-public import Mathlib.NumberTheory.Height.Northcott
 public import Mathlib.NumberTheory.Height.NumberField
 public import Mathlib.NumberTheory.Height.Projectivization
 public import Mathlib.NumberTheory.JacobiSum.Basic
@@ -6042,6 +6041,7 @@ public import Mathlib.Order.Monotone.Odd
 public import Mathlib.Order.Monotone.Union
 public import Mathlib.Order.Nat
 public import Mathlib.Order.NonemptyFiniteChains
+public import Mathlib.Order.Northcott
 public import Mathlib.Order.Notation
 public import Mathlib.Order.Nucleus
 public import Mathlib.Order.OmegaCompletePartialOrder

Mathlib/GroupTheory/Descent.lean

@@ -8,7 +8,7 @@ module
 public import Mathlib.Data.Real.Basic
 public import Mathlib.GroupTheory.Finiteness
 public import Mathlib.GroupTheory.Index
-public import Mathlib.NumberTheory.Height.Northcott
+public import Mathlib.Order.Northcott
 
 import Mathlib.Data.Set.Finite.Lemmas
 import Mathlib.Tactic.FieldSimp

Mathlib/NumberTheory/ArithmeticFunction/LFunction.lean

@@ -6,7 +6,7 @@ Authors: Thomas Browning
 module
 
 public import Mathlib.NumberTheory.ArithmeticFunction.Defs
-public import Mathlib.NumberTheory.Height.Northcott
+public import Mathlib.Order.Northcott
 public import Mathlib.RingTheory.PowerSeries.Basic
 public import Mathlib.RingTheory.PowerSeries.PiTopology
 public import Mathlib.RingTheory.PowerSeries.Substitution

…thlib/NumberTheory/Height/Northcott.lean Mathlib/Order/Northcott.leanMathlib/NumberTheory/Height/Northcott.lean renamed to Mathlib/Order/Northcott.lean Mathlib/NumberTheory/Height/Northcott.lean renamed to Mathlib/Order/Northcott.lean

@@ -6,7 +6,7 @@ Authors: Xavier Roblot
 module
 
 public import Mathlib.Data.ZMod.QuotientRing
-public import Mathlib.NumberTheory.Height.Northcott
+public import Mathlib.Order.Northcott
 public import Mathlib.RingTheory.DedekindDomain.Basic
 public import Mathlib.RingTheory.IntegralDomain
 public import Mathlib.RingTheory.Ideal.Norm.AbsNorm