stdlib tests: move JVM-only test source files

libraries/stdlib/jvm/test/text/StringBuilderJVMTest.kt

@@ -0,0 +1,22 @@
+@file:kotlin.jvm.JvmVersion
+package test.text
+
+import kotlin.test.*
+
+class StringBuilderJVMTest() {
+
+    @Test fun stringBuildWithInitialCapacity() {
+        val s = buildString(123) {
+            assertEquals(123, capacity())
+        }
+        assertEquals("", s)
+    }
+
+    @Test fun getAndSetChar() {
+        val sb = StringBuilder("abc")
+        sb[1] = 'z'
+
+        assertEquals("azc", sb.toString())
+        assertEquals('c', sb[2])
+    }
+}