[IR BE] Fix SharedVariableLowering

* make it able to detect shared vars under any declaration kind, not only IrFunction
 * Add & update tests

compiler/testData/codegen/box/objects/kt2663.kt

@@ -1,5 +1,3 @@
-// IGNORE_BACKEND: JVM_IR
-// IGNORE_BACKEND: JS_IR
 fun box() : String {
     var a = 1
 

compiler/testData/codegen/box/objects/kt2663_3.kt

@@ -0,0 +1,9 @@
+// IGNORE_BACKEND: JVM_IR
+fun box() : String {
+    var a = 1
+
+    object {
+        val t = run { a++ }
+    }
+    return if (a == 2) "OK" else "fail"
+}