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/wasm/test/testUtils.kt

@@ -31,3 +31,5 @@ actual val supportsSuppressedExceptions: Boolean get() = false
 
 // TODO: implement named group reference in replacement expression
 public actual val supportsNamedCapturingGroup: Boolean get() = false
+
+public actual val regexSplitUnicodeCodePointHandling: Boolean get() = TODO()