[PowerAssert] Add codegen tests

plugins/power-assert/testData/codegen/cast/InstanceEquals.box.txt

@@ -0,0 +1,4 @@
+Assertion failed
+assert(null is String)
+            |
+            false

plugins/power-assert/testData/codegen/cast/InstanceEquals.kt

@@ -0,0 +1,3 @@
+fun box() = expectThrowableMessage {
+    assert(null is String)
+}

plugins/power-assert/testData/codegen/cast/InstanceNotEquals.box.txt

@@ -0,0 +1,4 @@
+Assertion failed
+assert("Hello, world!" !is String)
+                       |
+                       false

plugins/power-assert/testData/codegen/cast/InstanceNotEquals.kt

@@ -0,0 +1,3 @@
+fun box() = expectThrowableMessage {
+    assert("Hello, world!" !is String)
+}

plugins/power-assert/testData/codegen/cast/SmartCast.box.txt

@@ -0,0 +1,8 @@
+Assertion failed
+assert(greeting is String && greeting.length == 2)
+       |        |            |        |      |
+       |        |            |        |      false
+       |        |            |        5
+       |        |            hello
+       |        true
+       hello

plugins/power-assert/testData/codegen/cast/SmartCast.kt

@@ -0,0 +1,4 @@
+fun box() = expectThrowableMessage {
+    val greeting: Any = "hello"
+    assert(greeting is String && greeting.length == 2)
+}