kotlinx.atomicfu compiler plugin for JS_IR backend (#4581)

* kotlinx.atomicfu compiler plugin for JS_IR

Support transformations of atomic operations introduced by the kotlinx.atomicfu library for the JS_IR backend. Compiler plugin is applied externally by the kotlinx.atomicfu gradle plugin.

* Apply compiler plugin for JS platform only

* New plugin test structure

* testGroupOutputDirPrefix changed

plugins/atomicfu/atomicfu-compiler/testData/box/IndexArrayElementGetterTest.kt

@@ -0,0 +1,32 @@
+import kotlinx.atomicfu.*
+import kotlin.test.*
+
+class IndexArrayElementGetterTest {
+    private val clazz = AtomicArrayClass()
+
+    fun fib(a: Int): Int = if (a == 0 || a == 1) a else fib(a - 1) + fib(a - 2)
+
+    fun testIndexArrayElementGetting() {
+        clazz.intArr[8].value = 3
+        val i = fib(4)
+        val j = fib(5)
+        assertEquals(clazz.intArr[i + j].value, 3)
+        assertEquals(clazz.intArr[fib(4) + fib(5)].value, 3)
+        clazz.longArr[3].value = 100
+        assertEquals(clazz.longArr[fib(6) - fib(5)].value, 100)
+        assertEquals(clazz.longArr[(fib(6) + fib(4)) % 8].value, 100)
+        assertEquals(clazz.longArr[(fib(6) + fib(4)) % 8].value, 100)
+        assertEquals(clazz.longArr[(fib(4) + fib(5)) % fib(5)].value, 100)
+    }
+
+    class AtomicArrayClass {
+        val intArr = AtomicIntArray(10)
+        val longArr = AtomicLongArray(10)
+    }
+}
+
+fun box(): String {
+    val testClass = IndexArrayElementGetterTest()
+    testClass.testIndexArrayElementGetting()
+    return "OK"
+}