Make DurationUnit not a typealias of TimeUnit on JVM

Provide conversion functions between DurationUnit and TimeUnit

libraries/stdlib/jvm/src/kotlin/time/DurationUnitJvm.kt

@@ -8,26 +8,79 @@
 
 package kotlin.time
 
+import java.util.concurrent.TimeUnit
+
 @SinceKotlin("1.6")
 @WasExperimental(ExperimentalTime::class)
-public actual typealias DurationUnit = java.util.concurrent.TimeUnit
+public actual enum class DurationUnit(internal val timeUnit: TimeUnit) {
+    /**
+     * Time unit representing one nanosecond, which is 1/1000 of a microsecond.
+     */
+    NANOSECONDS(TimeUnit.NANOSECONDS),
+    /**
+     * Time unit representing one microsecond, which is 1/1000 of a millisecond.
+     */
+    MICROSECONDS(TimeUnit.MICROSECONDS),
+    /**
+     * Time unit representing one millisecond, which is 1/1000 of a second.
+     */
+    MILLISECONDS(TimeUnit.MILLISECONDS),
+    /**
+     * Time unit representing one second.
+     */
+    SECONDS(TimeUnit.SECONDS),
+    /**
+     * Time unit representing one minute.
+     */
+    MINUTES(TimeUnit.MINUTES),
+    /**
+     * Time unit representing one hour.
+     */
+    HOURS(TimeUnit.HOURS),
+    /**
+     * Time unit representing one day, which is always equal to 24 hours.
+     */
+    DAYS(TimeUnit.DAYS);
+}
+
+/**
+ * Converts this [kotlin.time.DurationUnit][DurationUnit] enum value to the corresponding [java.util.concurrent.TimeUnit][java.util.concurrent.TimeUnit] value.
+ */
+@SinceKotlin("1.6")
+@ExperimentalTime
+public fun DurationUnit.toTimeUnit(): TimeUnit = timeUnit
+
+/**
+ * Converts this [java.util.concurrent.TimeUnit][java.util.concurrent.TimeUnit] enum value to the corresponding [kotlin.time.DurationUnit][DurationUnit] value.
+ */
+@SinceKotlin("1.6")
+@ExperimentalTime
+public fun TimeUnit.toDurationUnit(): DurationUnit = when (this) {
+    TimeUnit.NANOSECONDS -> DurationUnit.NANOSECONDS
+    TimeUnit.MICROSECONDS -> DurationUnit.MICROSECONDS
+    TimeUnit.MILLISECONDS -> DurationUnit.MILLISECONDS
+    TimeUnit.SECONDS -> DurationUnit.SECONDS
+    TimeUnit.MINUTES -> DurationUnit.MINUTES
+    TimeUnit.HOURS -> DurationUnit.HOURS
+    TimeUnit.DAYS -> DurationUnit.DAYS
+}
 
 @SinceKotlin("1.3")
 internal actual fun convertDurationUnit(value: Double, sourceUnit: DurationUnit, targetUnit: DurationUnit): Double {
-    val sourceInTargets = targetUnit.convert(1, sourceUnit)
+    val sourceInTargets = targetUnit.timeUnit.convert(1, sourceUnit.timeUnit)
     if (sourceInTargets > 0)
         return value * sourceInTargets
 
-    val otherInThis = sourceUnit.convert(1, targetUnit)
+    val otherInThis = sourceUnit.timeUnit.convert(1, targetUnit.timeUnit)
     return value / otherInThis
 }
 
 @SinceKotlin("1.5")
 internal actual fun convertDurationUnitOverflow(value: Long, sourceUnit: DurationUnit, targetUnit: DurationUnit): Long {
-    return targetUnit.convert(value, sourceUnit)
+    return targetUnit.timeUnit.convert(value, sourceUnit.timeUnit)
 }
 
 @SinceKotlin("1.5")
 internal actual fun convertDurationUnit(value: Long, sourceUnit: DurationUnit, targetUnit: DurationUnit): Long {
-    return targetUnit.convert(value, sourceUnit)
+    return targetUnit.timeUnit.convert(value, sourceUnit.timeUnit)
 }