Prepare to hide native specific regex methods from public API

backend.native/tests/harmony_regex/PatternTest2.kt

@@ -32,13 +32,11 @@ class PatternTest2 {
 
         var testString = "foo123"
         assertTrue(regex.matches(testString))
-        assertTrue(regex.containsMatchIn(testString, 0))
-        assertTrue(regex.lookingAt(testString))
+        assertTrue(regex in testString)
 
         testString = "fox"
         assertFalse(regex.matches(testString))
-        assertFalse(regex.containsMatchIn(testString, 0))
-        assertFalse(regex.lookingAt(testString))
+        assertFalse(regex in testString)
 
         assertTrue(Regex("foo.*").matches("foo123"))
         assertFalse(Regex("foo.*").matches("fox"))
@@ -880,7 +878,7 @@ class PatternTest2 {
     @Test fun testCompile2() {
         val findString = "\\Qimport\\E"
         val regex = Regex(findString)
-        regex.containsMatchIn("import a.A;\n\n import b.B;\nclass C {}", 0)
+        assertTrue(regex in "import a.A;\n\n import b.B;\nclass C {}")
     }
 
     @Test fun testCompile3() {

runtime/src/main/kotlin/kotlin/text/Regex.kt

@@ -256,6 +256,7 @@ public actual class Regex internal constructor(internal val nativePattern: Patte
      *
      * @param replacement A replacement expression that can include substitutions.
      */
+    @Suppress("DEPRECATION_ERROR")
     actual fun replaceFirst(input: CharSequence, replacement: String): String
             = replaceFirst(input) { match -> processReplacement(match, replacement) }
 
@@ -297,9 +298,11 @@ public actual class Regex internal constructor(internal val nativePattern: Patte
     override fun toString(): String = nativePattern.toString()
 
     // Native specific =================================================================================================
+    @Deprecated("The function is going to be removed from public API", level = DeprecationLevel.ERROR)
     fun lookingAt(input: CharSequence): Boolean = doMatch(input, Mode.FIND) != null
 
     /** Indicates whether the regular expression can find at least one match in the specified [input] starting with [index]. */
+    @Deprecated("The function is going to be removed from public API", level = DeprecationLevel.ERROR)
     fun containsMatchIn(input: CharSequence, index: Int): Boolean = find(input, index) != null
 
     /**
@@ -307,6 +310,7 @@ public actual class Regex internal constructor(internal val nativePattern: Patte
      * the given function [transform] that takes a [MatchResult] representing the occurrence and returns a string to be used as a
      * replacement for that occurrence.
      */
+    @Deprecated("The function is going to be removed from public API", level = DeprecationLevel.ERROR)
     fun replaceFirst(input: CharSequence, transform: (MatchResult) -> CharSequence): String {
         val match = find(input) ?: return input.toString()
         val length = input.length