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/LockFreeLongCounterTest.kt

@@ -0,0 +1,61 @@
+import kotlinx.atomicfu.*
+import kotlin.test.*
+
+class LockFreeLongCounterTest {
+    private inline fun testWith(g: LockFreeLongCounter.() -> Long) {
+        val c = LockFreeLongCounter()
+        check(c.g() == 0L)
+        check(c.increment() == 1L)
+        check(c.g() == 1L)
+        check(c.increment() == 2L)
+        check(c.g() == 2L)
+    }
+
+    fun testBasic() = testWith { get() }
+
+    fun testGetInner() = testWith { getInner() }
+
+    fun testAdd2() {
+        val c = LockFreeLongCounter()
+        c.add2()
+        check(c.get() == 2L)
+        c.add2()
+        check(c.get() == 4L)
+    }
+
+    fun testSetM2() {
+        val c = LockFreeLongCounter()
+        c.setM2()
+        check(c.get() == -2L)
+    }
+}
+
+class LockFreeLongCounter {
+    private val counter = atomic(0L)
+
+    fun get(): Long = counter.value
+
+    fun increment(): Long = counter.incrementAndGet()
+
+    fun add2() = counter.getAndAdd(2)
+
+    fun setM2() {
+        counter.value = -2L // LDC instruction here
+    }
+
+    fun getInner(): Long = Inner().getFromOuter()
+
+    // testing how an inner class can get access to it
+    private inner class Inner {
+        fun getFromOuter(): Long = counter.value
+    }
+}
+
+fun box(): String {
+    val testClass = LockFreeLongCounterTest()
+    testClass.testBasic()
+    testClass.testAdd2()
+    testClass.testSetM2()
+    testClass.testGetInner()
+    return "OK"
+}