[test] Move irJsText tests to irText directory

So that all irText tests could be found in one place

compiler/testData/ir/irText/js/dynamic/dynamicArrayIncrementDecrement.kt

@@ -0,0 +1,8 @@
+// FIR_IDENTICAL
+
+fun testArrayIncrementDecrement(d: dynamic) {
+    val t1 = ++d["prefixIncr"]
+    val t2 = --d["prefixDecr"]
+    val t3 = d["postfixIncr"]++
+    val t4 = d["postfixDecr"]--
+}