Resolves the interaction of @JvmOverloads annotations and
parameterless main methods.
In the following code, both mechanisms generate methods that
ultimately produce the signature `public static void main(String[] args)`
of which there can be only one (true in general of any signature).
```
fun main() { }
@JvmOverloads
fun main(Array<String> args, x: Int = 42) { }
```
This PR simply shuffles the lowerings around, letting parameterless
main methods detect the presence of the default overload produced by
the annotation.
Additionally, this PR improves the testing of parameterless main
methods by actual bytecode patterns, and not simple check for
successful compilation (as @sfs and I discovered, there are issues in
flagging an error on duplicate signatures on the IR backend).
This commit:
- introduces tests explicating what is and isn't considered a
proper main method on the JVM backends.
- implements support for parameterless main methods on the JVM IR
backend
- See KT-34338 for more tests.
