RFR: 8357016: Candidate main methods not computed properly [v4]

[Jan Lahoda]

> A consider class like this:
> 
> 
> public class TwoMains {
>     private static void main(String... args) {}
>     static void main() {
>         System.out.println("Should be called, but is not.");
>     }
> }
> 
> 
> The `MethodFinder` will do lookup for the `main(String[])` method, and it finds one, so does not proceed with a lookup for `main()`. But then, it will check the access modifier, and will reject that method, never going back to the `main()` method. This is not what the JLS says about the lookup - the private method is not a candidate, and should be ignored.
> 
> Something similar happens if the return type is not `void`.
> 
> This PR is fixing that by checking whether the `main(String[])` method is usable early, and falling back to `main()` if it `main(String[])` is not usable.
> 
> It also removes the check for the `abstract` method, as that, by itself, is not really backed by JLS, but adds a check for `abstract` class, producing a user-friendly message is trying to invoke an instance `main` method on an `abstract` class (which, obviously, cannot be instantiated).

Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:

  Adjusting message and tests.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/25256/files
  - new: https://git.openjdk.org/jdk/pull/25256/files/f63dab37..db7e7ceb

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25256&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25256&range=02-03

  Stats: 3 lines in 3 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/25256.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25256/head:pull/25256

PR: https://git.openjdk.org/jdk/pull/25256