Move StringBuilder to its own file

libraries/stdlib/common/src/kotlin/TextH.kt

@@ -5,22 +5,6 @@
 
 package kotlin.text
 
-expect class StringBuilder : Appendable, CharSequence {
-    constructor()
-    constructor(capacity: Int)
-    constructor(content: CharSequence)
-
-    override val length: Int
-    override operator fun get(index: Int): Char
-    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence
-
-    fun reverse(): StringBuilder
-    override fun append(c: Char): StringBuilder
-    override fun append(csq: CharSequence?): StringBuilder
-    override fun append(csq: CharSequence?, start: Int, end: Int): StringBuilder
-    fun append(obj: Any?): StringBuilder
-}
-
 expect class Regex {
     constructor(pattern: String)
     constructor(pattern: String, option: RegexOption)
@@ -225,15 +209,6 @@ public expect fun String.decapitalize(): String
 public expect fun CharSequence.repeat(n: Int): String
 
 
-/**
- * Clears the content of this string builder making it empty.
- *
- * @sample samples.text.Strings.clearStringBuilder
- */
-@SinceKotlin("1.3")
-public expect fun StringBuilder.clear(): StringBuilder
-
-
 /**
  * Returns a new string with all occurrences of [oldChar] replaced with [newChar].
  */

libraries/stdlib/src/kotlin/text/StringBuilder.kt

@@ -8,6 +8,30 @@
 
 package kotlin.text
 
+expect class StringBuilder : Appendable, CharSequence {
+    constructor()
+    constructor(capacity: Int)
+    constructor(content: CharSequence)
+
+    override val length: Int
+    override operator fun get(index: Int): Char
+    override fun subSequence(startIndex: Int, endIndex: Int): CharSequence
+
+    fun reverse(): StringBuilder
+    override fun append(c: Char): StringBuilder
+    override fun append(csq: CharSequence?): StringBuilder
+    override fun append(csq: CharSequence?, start: Int, end: Int): StringBuilder
+    fun append(obj: Any?): StringBuilder
+}
+
+/**
+ * Clears the content of this string builder making it empty.
+ *
+ * @sample samples.text.Strings.clearStringBuilder
+ */
+@SinceKotlin("1.3")
+public expect fun StringBuilder.clear(): StringBuilder
+
 /**
  * Builds new string by populating newly created [StringBuilder] using provided [builderAction]
  * and then converting it to [String].