named tuple toMap extension method (#23827)

There already are methods `toArray, toList` for `NamedTuple` for
collecting elements into collections.
I would like to add method `toSeqMap` where keys are names of the
elements.

For example:
```scala
(x = 1, y = true).toSeqMap // SeqMap("x" -> 1, "y" -> true)
```

One obvious usage of this method is debugging code with named tuples
(standard `toString` method doesn't show names):
```scala
println((x = 1, y = true)) // prints (1, true)
println((x = 1, y = true).toSeqMap) // prints SeqMap(x -> 1, y -> true)
```

Author: bracevac

library/src/scala/NamedTuple.scala

@@ -1,5 +1,6 @@
 package scala
 import compiletime.ops.boolean.*
+import collection.immutable.{SeqMap, ListMap}
 
 import language.experimental.captureChecking
 
@@ -30,7 +31,7 @@ object NamedTuple:
   import NamedTupleDecomposition.{Names, DropNames}
   export NamedTupleDecomposition.{
     Names, DropNames,
-    apply, size, init, head, last, tail, take, drop, splitAt, ++, map, reverse, zip, toList, toArray, toIArray
+    apply, size, init, head, last, tail, take, drop, splitAt, ++, map, reverse, zip, toList, toArray, toIArray, toSeqMap
   }
 
   extension [N <: Tuple, V <: Tuple](x: NamedTuple[N, V])
@@ -209,6 +210,15 @@ object NamedTupleDecomposition:
     /** An immutable array consisting of all element values */
     inline def toIArray: IArray[Object] = x.toTuple.toIArray
 
+    /** An immutable map consisting of all element values preserving the order of fields.
+     *  Keys are the names of the elements.
+     */
+    inline def toSeqMap: SeqMap[String, Tuple.Union[V]] =
+      inline compiletime.constValueTuple[N].toList match
+        case names: List[String] =>
+          ListMap.from(names.iterator.zip(
+            x.toTuple.productIterator.asInstanceOf[Iterator[Tuple.Union[V]]]
+          ))
   end extension
 
   /** The names of a named tuple, represented as a tuple of literal string values. */

tests/run/named-tuple-ops.scala

@@ -1,5 +1,6 @@
 //> using options -source future
 import scala.compiletime.asMatchable
+import scala.collection.immutable.{ListMap, SeqMap}
 
 type City = (name: String, zip: Int, pop: Int)
 type Raw = (String, Int, Int)
@@ -82,7 +83,9 @@ type Labels = (x: String, y: String)
   val _: List[String | Int] = cityFields
   assert(cityFields == List("Lausanne", 1000, 140000))
 
-  val citArr = city.toArray
-  val _: List[String | Int] = cityFields
-  assert(cityFields == List("Lausanne", 1000, 140000))
+  val cityArr = city.toArray
+  assert(cityArr.sameElements(Array("Lausanne", 1000, 140000)))
 
+  val cityMap = city.toSeqMap
+  val _: SeqMap[String, String | Int] = cityMap
+  assert(cityMap == ListMap("name" -> "Lausanne", "zip" -> 1000, "pop" -> 140000))