Rename Pattern to Regex.

toRegex now converts string to our regex, and toPattern converts to JVM Pattern.

libraries/stdlib/test/text/RegexJVMTest.kt

@@ -0,0 +1,30 @@
+package test.text
+
+import kotlin.test.*
+import kotlin.text.*
+import org.junit.Test as test
+
+
+class RegexJVMTest {
+
+    test fun matchGroups() {
+        val input = "1a 2b 3c"
+        val regex = "(\\d)(\\w)".toRegex()
+
+        val matches = regex.matchAll(input).toList()
+        assertTrue(matches.all { it.groups.size() == 3 })
+        val m1 = matches[0]
+        assertEquals("1a", m1.groups[0]?.value)
+        assertEquals(0..1, m1.groups[0]?.range)
+        assertEquals("1", m1.groups[1]?.value)
+        assertEquals(0..0, m1.groups[1]?.range)
+        assertEquals("a", m1.groups[2]?.value)
+        assertEquals(1..1, m1.groups[2]?.range)
+
+        val m2 = matches[1]
+        assertEquals("2", m2.groups[1]?.value)
+        assertEquals(3..3, m2.groups[1]?.range)
+        assertEquals("b", m2.groups[2]?.value)
+        assertEquals(4..4, m2.groups[2]?.range)
+    }
+}