JS: create new common directory for all generated tests, migrate several tests there

js/js.translator/testData/box/char/charUnaryOperations.kt

@@ -0,0 +1,25 @@
+package foo
+
+fun box(): String {
+
+    var x: Char = 'A'
+    x++
+    assertEquals('B', x)
+    ++x
+    assertEquals('C', x)
+
+    var y = x++
+    assertEquals('C', y)
+    assertEquals('D', x)
+
+    y = ++x
+    assertEquals('E', y)
+    assertEquals('E', x)
+
+    x--
+    assertEquals('D', x)
+    --x
+    assertEquals('C', x)
+
+    return "OK"
+}