[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/helloAppVarargMainIR/hello.run.expected

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