Transform some builtin methods

1. CharSequence.charAt -> get
2. ML.remove(Int) -> removeAt,
3. MC.remove(Any?) -> MC.remove(E)

core/builtins/native/kotlin/CharSequence.kt

@@ -28,7 +28,7 @@ public interface CharSequence {
     /**
      * Returns the character at the specified [index] in the sequence.
      */
-    public fun charAt(index: Int): Char
+    public operator fun get(index: Int): Char
 
     /**
      * Returns a subsequence of this sequence.

core/builtins/native/kotlin/Collections.kt

@@ -91,7 +91,7 @@ public interface MutableCollection<E> : Collection<E>, MutableIterable<E> {
      *
      * @return `true` if the element has been successfully removed; `false` if it was not present in the collection.
      */
-    public fun remove(o: Any?): Boolean
+    public fun remove(o: E): Boolean
 
     // Bulk Modification Operations
     /**
@@ -181,7 +181,7 @@ public interface List<out E> : Collection<E> {
 public interface MutableList<E> : List<E>, MutableCollection<E> {
     // Modification Operations
     override fun add(e: E): Boolean
-    override fun remove(o: Any?): Boolean
+    override fun remove(o: E): Boolean
 
     // Bulk Modification Operations
     override fun addAll(c: Collection<E>): Boolean
@@ -214,7 +214,7 @@ public interface MutableList<E> : List<E>, MutableCollection<E> {
      *
      * @return the element that has been removed.
      */
-    public fun remove(index: Int): E
+    public fun removeAt(index: Int): E
 
     // List Iterators
     override fun listIterator(): MutableListIterator<E>
@@ -252,7 +252,7 @@ public interface MutableSet<E> : Set<E>, MutableCollection<E> {
 
     // Modification Operations
     override fun add(e: E): Boolean
-    override fun remove(o: Any?): Boolean
+    override fun remove(o: E): Boolean
 
     // Bulk Modification Operations
     override fun addAll(c: Collection<E>): Boolean

core/builtins/native/kotlin/String.kt

@@ -28,14 +28,9 @@ public class String : Comparable<String>, CharSequence {
      */
     public operator fun plus(other: Any?): String
 
-    /**
-     * Returns the character at the specified [index].
-     */
-    public operator fun get(index: Int): Char
-
     public override fun length(): Int
 
-    public override fun charAt(index: Int): Char
+    public override fun get(index: Int): Char
 
     public override fun subSequence(start: Int, end: Int): CharSequence