Bring back Duration construction extensions KT-46229

Return the extension properties for constructing Duration from numbers,
but this time place them in Duration.Companion rather than on top-level.

- provide the new set of construction extension properties
  in companion of Duration
- leave top-level extension properties experimental,
  increase their deprecation level to ERROR,
  propose the extension properties in companion instead.
- leave Duration companion static factory functions experimental,
  deprecate them and propose the extension properties in companion instead.

libraries/stdlib/jdk8/test/time/DurationConversionTest.kt

@@ -8,6 +8,9 @@ package kotlin.jdk8.time.test
 import kotlin.random.Random
 import kotlin.test.*
 import kotlin.time.*
+import kotlin.time.Duration.Companion.days
+import kotlin.time.Duration.Companion.nanoseconds
+import kotlin.time.Duration.Companion.seconds
 import java.time.Duration as JTDuration
 
 class DurationConversionTest {
@@ -15,7 +18,7 @@ class DurationConversionTest {
     fun twoWayConversion() {
         fun test(days: Int, hours: Int, minutes: Int, seconds: Int, millis: Int, nanos: Int) {
             val duration = with(Duration) {
-                days(days) + hours(hours) + minutes(minutes) + seconds(seconds) + milliseconds(millis) + nanoseconds(nanos)
+                days.days + hours.hours + minutes.minutes + seconds.seconds + millis.milliseconds + nanos.nanoseconds
             }
             val jtDuration = JTDuration.ZERO
                 .plusDays(days.toLong())
@@ -50,12 +53,12 @@ class DurationConversionTest {
         val duration1 = jtDuration1.toKotlinDuration()
         val duration2 = jtDuration1.toKotlinDuration()
         assertEquals(duration1, duration2)
-        assertEquals(Duration.days(365 * 150), duration2)
+        assertEquals((365 * 150).days, duration2)
     }
 
     @Test
     fun kotlinToJavaClamping() {
-        val duration = Duration.seconds(Long.MAX_VALUE) * 5
+        val duration = Long.MAX_VALUE.seconds * 5
         val jtDuration = duration.toJavaDuration()
         assertEquals(JTDuration.ofSeconds(Long.MAX_VALUE), jtDuration)
 
@@ -66,7 +69,7 @@ class DurationConversionTest {
     @Test
     fun randomIsoConversionEquivalence() {
         repeat(100) {
-            val duration = Duration.nanoseconds(Random.nextLong(-(1L shl 53) + 1, 1L shl 53))
+            val duration = Random.nextLong(-(1L shl 53) + 1, 1L shl 53).nanoseconds
             val fromString = JTDuration.parse(duration.toIsoString())
             val fromDuration = duration.toJavaDuration()