TimeZone.of("z") should work the same as calling from capital "Z" #530 (#530)

Fixes #529

Author: DmitryNekrasov

core/common/test/TimeZoneTest.kt

@@ -111,6 +111,7 @@ class TimeZoneTest {
             Pair("Europe/Paris", "Europe/Paris"),
             Pair("Europe/Berlin", "Europe/Berlin"),
             Pair("Z", "Z"),
+            Pair("z", "Z"),
             Pair("UTC", "UTC"),
             Pair("UTC+01:00", "UTC+01:00"),
             Pair("GMT+01:00", "GMT+01:00"),

core/common/test/format/DateTimeComponentsFormatTest.kt

@@ -331,11 +331,7 @@ class DateTimeComponentsFormatTest {
 
     @Test
     fun testZuluTimeZone() {
-        // Replace it to:
-        // listOf("z", "Z").forEach(::assertParseableAsTimeZone)
-        // when TimeZone.of("z") works correctly
-        assertParseableAsTimeZone("Z")
-        assertIncorrectlyParseableAsTimeZone("z")
+        listOf("z", "Z").forEach(::assertParseableAsTimeZone)
     }
 
     @Test

core/commonKotlin/src/TimeZone.kt

@@ -32,7 +32,7 @@ public actual open class TimeZone internal constructor() {
             if (zoneId == "UTC") {
                 return UTC
             }
-            if (zoneId == "Z") {
+            if (zoneId == "Z" || zoneId == "z") {
                 return UtcOffset.ZERO.asTimeZone()
             }
             if (zoneId == "SYSTEM") {

core/jvm/src/TimeZoneJvm.kt

@@ -36,7 +36,7 @@ public actual open class TimeZone internal constructor(internal val zoneId: Zone
             FixedOffsetTimeZone(UtcOffset.ZERO, ZoneId.of("UTC"))
 
         public actual fun of(zoneId: String): TimeZone = try {
-            ofZone(ZoneId.of(zoneId))
+            ofZone(ZoneId.of(if (zoneId == "z") "Z" else zoneId))
         } catch (e: Exception) {
             if (e is DateTimeException) throw IllegalTimeZoneException(e)
             throw e