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/LockFreeIntBitsTest.kt

@@ -0,0 +1,57 @@
+import kotlinx.atomicfu.*
+import kotlin.test.*
+
+class LockFreeIntBitsTest {
+    fun testBasic() {
+        val bs = LockFreeIntBits()
+        check(!bs[0])
+        check(bs.bitSet(0))
+        check(bs[0])
+        check(!bs.bitSet(0))
+
+        check(!bs[1])
+        check(bs.bitSet(1))
+        check(bs[1])
+        check(!bs.bitSet(1))
+        check(!bs.bitSet(0))
+
+        check(bs[0])
+        check(bs.bitClear(0))
+        check(!bs.bitClear(0))
+
+        check(bs[1])
+    }
+}
+
+class LockFreeIntBits {
+    private val bits = atomic(0)
+
+    private fun Int.mask() = 1 shl this
+
+    operator fun get(index: Int): Boolean = bits.value and index.mask() != 0
+
+    // User-defined private inline function
+    private inline fun bitUpdate(check: (Int) -> Boolean, upd: (Int) -> Int): Boolean {
+        bits.update {
+            if (check(it)) return false
+            upd(it)
+        }
+        return true
+    }
+
+    fun bitSet(index: Int): Boolean {
+        val mask = index.mask()
+        return bitUpdate({ it and mask != 0 }, { it or mask })
+    }
+
+    fun bitClear(index: Int): Boolean {
+        val mask = index.mask()
+        return bitUpdate({ it and mask == 0 }, { it and mask.inv() })
+    }
+}
+
+fun box(): String {
+    val testClass = LockFreeIntBitsTest()
+    testClass.testBasic()
+    return "OK"
+}