Move convertDurationUnit into Duration companion

libraries/stdlib/test/time/DurationTest.kt

@@ -52,7 +52,7 @@ class DurationTest {
             repeat(10) {
                 val d1 = value.toDuration(unit)
                 val unit2 = units.random()
-                val value2 = convertDurationUnit(value, unit, unit2)
+                val value2 = Duration.convert(value, unit, unit2)
                 val d2 = value2.toDuration(unit2)
                 assertEquals(d1, d2, "$value $unit in $unit2")
                 assertEquals(d1.hashCode(), d2.hashCode())
@@ -124,7 +124,7 @@ class DurationTest {
             val unit = units.random()
             val unit2 = units.random()
 
-            assertAlmostEquals(convertDurationUnit(value.toDouble(), unit, unit2), value.toDuration(unit).toDouble(unit2))
+            assertAlmostEquals(Duration.convert(value.toDouble(), unit, unit2), value.toDuration(unit).toDouble(unit2))
         }
     }
 

libraries/stdlib/test/time/DurationUnitTest.kt

@@ -22,11 +22,11 @@ class DurationUnitTest {
     fun conversion() {
         fun test(sourceValue: Double, sourceUnit: DurationUnit, targetValue: Double, targetUnit: DurationUnit) {
             assertEquals(
-                targetValue, convertDurationUnit(sourceValue, sourceUnit, targetUnit),
+                targetValue, Duration.convert(sourceValue, sourceUnit, targetUnit),
                 "Expected $sourceValue $sourceUnit to be $targetValue $targetUnit"
             )
             assertEquals(
-                sourceValue, convertDurationUnit(targetValue, targetUnit, sourceUnit),
+                sourceValue, Duration.convert(targetValue, targetUnit, sourceUnit),
                 "Expected $targetValue $targetUnit to be $sourceValue $sourceUnit"
             )
         }