[WIP] Add Compiler Smoke Tests for (suspend) main methods

This commit ports the (parameterless) main integration tests in
`CompilerSmokeTest` to the IR backend. It also includes a simple
suspend main test.

The advanced ones (like `helloAppSuspendParameterlessMain`) are
currently blocked by pending changes to capturing suspend lambdas,
which are underway.

compiler/testData/integration/smoke/helloAppParameterlessMainIR/hello.compile.expected

@@ -0,0 +1 @@
+Return code: 0

compiler/testData/integration/smoke/helloAppParameterlessMainIR/hello.kt

@@ -0,0 +1,5 @@
+package Hello
+
+fun main() {
+    System.out.println("Hello!")
+}

compiler/testData/integration/smoke/helloAppParameterlessMainIR/hello.run.expected

@@ -0,0 +1,4 @@
+OUT:
+Hello!
+
+Return code: 0