Allow to compile Scala 2.11 scalalib with JDK 17 (#2530)

* Added methods needed to compile Scala 2.11 scalalib using JDK 17

scalalib/overrides-2.11/scala/collection/mutable/StringBuilder.scala.patch

@@ -0,0 +1,33 @@
+--- 2.11.12/scala/collection/mutable/StringBuilder.scala	2022-01-14 13:49:05.000000000 +0200
++++ overrides-2.11.12/scala/collection/mutable/StringBuilder.scala	2022-01-14 13:47:55.000000000 +0200
+@@ -14,6 +14,14 @@
+ import scala.annotation.migration
+ import immutable.StringLike
+
++// used for compilation of scala-native with jdk8, when
++//  we need to have isEmpty overrided, for building with jdk17
++trait StringBuilderIsEmptyProvider {
++
++  def isEmpty: Boolean
++
++}
++
+ /** A builder for mutable sequence of characters.  This class provides an API
+  *  mostly compatible with `java.lang.StringBuilder`, except where there are
+  *  conflicts with the Scala collections API (such as the `reverse` method.)
+@@ -34,6 +42,7 @@
+          with IndexedSeq[Char]
+          with StringLike[StringBuilder]
+          with Builder[Char, String]
++         with StringBuilderIsEmptyProvider
+          with Serializable {
+
+   override protected[this] def thisCollection: StringBuilder = this
+@@ -72,6 +81,7 @@
+     arr
+   }
+
++  override def isEmpty: Boolean = underlying.length()==0
+   override def length: Int = underlying.length()
+   def length_=(n: Int) { underlying.setLength(n) }
+