KT-49721 Avoid matching from the same position after a zero-width match

In JS, RegExp can return a match before the specified start index,
if it has matched at that index, but it is in the middle of a surrogate
pair. Account for that when advancing to the next position after
a zero-width match so that it doesn't get to the middle of SP.

libraries/stdlib/test/text/RegexTest.kt

@@ -7,6 +7,7 @@
 
 package test.text
 
+import test.regexSplitUnicodeCodePointHandling
 import test.supportsNamedCapturingGroup
 import kotlin.test.*
 
@@ -354,6 +355,11 @@ class RegexTest {
 
         testSplitEquals("".split(""), "", emptyMatch)
 
+        testSplitEquals(
+            if (regexSplitUnicodeCodePointHandling) listOf("", "\uD83D\uDE04", "\uD801", "") else listOf("", "\uD83D", "\uDE04", "\uD801", ""),
+            "\uD83D\uDE04\uD801", emptyMatch
+        )
+
         val emptyMatchBeforeT = "(?=t)".toRegex()
 
         testSplitEquals(listOf("", "tes", "t"), input, emptyMatchBeforeT)
@@ -397,4 +403,16 @@ class RegexTest {
         assertFailsWith<NoSuchElementException> { splits.next() }
     }
 
+    @Test fun findAllEmoji() {
+        val input = "\uD83D\uDE04\uD801x"
+        val regex = ".".toRegex()
+
+        val matches = regex.findAll(input).toList()
+        val values = matches.map { it.value }
+        val ranges = matches.map { it.range }
+
+        assertEquals(listOf("\uD83D\uDE04", "\uD801", "x"), values)
+        assertEquals(listOf(0..1, 2..2, 3..3), ranges)
+    }
+
 }