support deserializing Scala Iterators

This is open just for discussion. jackson-module-scala can serialize Iterators but will fail if you try to deserialize them.

Noone has complained yet.

Most users would use standard collections when it comes to supporting Array-like data types.

Example test:

```
package com.fasterxml.jackson.module.scala.deser

import com.fasterxml.jackson.module.scala.DefaultScalaModule
import com.fasterxml.jackson.module.scala.introspect.ScalaAnnotationIntrospectorModule
import org.scalatest.BeforeAndAfterEach

object IteratorWithNumberDeserializerTest {
case class IteratorLong(longs: Iterator[Long])
case class IteratorJavaLong(longs: Iterator[java.lang.Long])
case class IteratorBigInt(longs: Iterator[BigInt])
}

class IteratorWithNumberDeserializerTest extends DeserializerTest with BeforeAndAfterEach {
lazy val module: DefaultScalaModule.type = DefaultScalaModule
import IteratorWithNumberDeserializerTest._

private def sumIteratorLong(v: Iterator[Long]): Long = v.sum
private def sumIteratorJavaLong(v: Iterator[java.lang.Long]): Long = v.map(_.toLong).sum
private def sumIteratorBigInt(v: Iterator[BigInt]): Long = v.sum.toLong

"JacksonModuleScala" should "deserialize IteratorLong" in {
ScalaAnnotationIntrospectorModule.registerReferencedValueType(classOf[IteratorLong], "longs", classOf[Long])
try {
val v1 = deserialize("""{"longs":[151,152,153]}""", classOf[IteratorLong])
v1 shouldBe IteratorLong(Iterator(151L, 152L, 153L))
//this will next call will fail with a Scala unboxing exception unless you ScalaAnnotationIntrospectorModule.registerReferencedValueType
//or use one of the equivalent classes in SeqWithNumberDeserializerTest
sumIteratorLong(v1.longs) shouldBe 456L
} finally {
ScalaAnnotationIntrospectorModule.clearRegisteredReferencedTypes()
}
}

it should "deserialize IteratorJavaLong" in {
val v1 = deserialize("""{"longs":[151,152,153]}""", classOf[IteratorJavaLong])
v1 shouldBe IteratorJavaLong(Iterator(151L, 152L, 153L))
sumIteratorJavaLong(v1.longs) shouldBe 456L
}

it should "deserialize IteratorBigInt" in {
val v1 = deserialize("""{"longs":[151,152,153]}""", classOf[IteratorBigInt])
v1 shouldBe IteratorBigInt(Iterator(151L, 152L, 153L))
sumIteratorBigInt(v1.longs) shouldBe 456L
}
}
```

Exception looks like:
```
Cannot find a Value deserializer for abstract type [collection-like type; class scala.collection.Iterator, contains [simple type, class long]]
at [Source: (String)"{"longs":[151,152,153]}"; line: 1, column: 1]
com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot find a Value deserializer for abstract type [collection-like type; class scala.collection.Iterator, contains [simple type, class long]]
```

Start with the IteratorWithNumberDeserializerTest example in the issue and run it to reproduce the InvalidDefinitionException. Inspect the existing Scala collection deserialization support around DefaultScalaModule and related sequence tests; done means the three shown Iterator cases deserialize and their sums equal 456.

Written by the indexing model from the issue text.