`Slf4JLoggerFactory` does not initialize when using no-op logger

Below is the full issue description. Here is a short description of why this happens:

Looking at the code, Slf4JLoggerFactory.INSTANCE should not care whether the slf4j implementation is a NOPLoggerFactory. The package-private INSTANCE_WITH_NOP_CHECK has that additional check, but INSTANCE does not. However, because the INSTANCE_WITH_NOP_CHECK is a static field, the nop check failing leads to the entire Slf4JLoggerFactory class failing to initialize, leading to the error below.

My suggestion would be to either revert the change that made the nop check instance a singleton (#11253), or (probably preferred) to move the singleton to a nested class so that the failure does not affect the outer class.

I can make a PR to fix this issue, however I will have to get new CLA approval since I changed employment since I last signed the CLA, which may take a few days.

Expected behavior

InternalLoggerFactory.setDefaultFactory(Slf4JLoggerFactory.INSTANCE);

should always succeed.

Actual behavior

When slf4j uses the noop logger, the code throws an exception:

Exception in thread "main" java.lang.NoClassDefFoundError: NOPLoggerFactory not supported
	at io.netty.util.internal.logging.Slf4JLoggerFactory.<init>(Slf4JLoggerFactory.java:45)
	at io.netty.util.internal.logging.Slf4JLoggerFactory.<clinit>(Slf4JLoggerFactory.java:33)
	at Main.main(Main.java:6)

Steps to reproduce

1. Create a new project with the org.slf4j:slf4j-api:1.7.32 and io.netty:netty-all:4.1.71.Final dependencies
2. Add the reproducer code from below
3. Run the main class

Minimal yet complete reproducer code (or URL to code)

import io.netty.util.internal.logging.InternalLoggerFactory;
import io.netty.util.internal.logging.Slf4JLoggerFactory;

public class Main {
    public static void main(String[] args) {
        InternalLoggerFactory.setDefaultFactory(Slf4JLoggerFactory.INSTANCE);
    }
}

Netty version

4.1.71.Final

JVM version (e.g. java -version)

Adopt OpenJDK 11.0.12

OS version (e.g. uname -a)

Linux yawkat-oracle 5.13.0-22-generic #22-Ubuntu SMP Fri Nov 5 13:21:36 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

[laosijikaichele]

@yawkat I created a PR: https://github.com/netty/netty/pull/11931.

[yawkat]

Sure, just may take a bit before I get the CLA approval, and because of holidays.