Change package of extensions and other top-level declarations from kotlin.js to kotlin to match corresponding ones in stdlib for JVM.

js/js.libraries/src/core/char.kt

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package kotlin.js
+package kotlin
 
 // actually \s is enough to match all whitespace, but \xA0 added because of different regexp behavior of Rhino used in Selenium tests
 public fun Char.isWhitespace(): Boolean = toString().matches("[\\s\\xA0]")

js/js.libraries/src/core/string.kt

@@ -1,4 +1,4 @@
-package kotlin.js
+package kotlin
 
 import kotlin.text.js.RegExp
 

js/js.libraries/src/core/stringsCode.kt

@@ -1,4 +1,4 @@
-package kotlin.js
+package kotlin
 
 import kotlin.text.Regex
 import kotlin.text.js.RegExp