Log4j2Metrics does not work with multiple registries and non-root loggers

[shakuzen]

While reading the code while looking at #5810 I saw another issue in this fix (or rather, this does not fully support binding to multiple MeterRegistry). The issue is that it only works on rootLoggerConfig, for all other logger configs the second filter will not be added.

Here is a modified test from the test added in this PR that does not pass as the non-root logger configuration is not tracked for the second MeterRegistry:

    @Test
    void multipleRegistriesCanBeBound() {
        LoggerContext loggerContext = new LoggerContext("test");

        LoggerConfig loggerConfig = new LoggerConfig("com.test", Level.INFO, false);
        Configuration configuration = loggerContext.getConfiguration();
        configuration.getRootLogger().setLevel(Level.INFO);
        configuration.addLogger("com.test", loggerConfig);
        loggerContext.updateLoggers(configuration);

        MeterRegistry registry2 = new SimpleMeterRegistry();

        Log4j2Metrics log4j2Metrics = new Log4j2Metrics(emptyList(), loggerContext);
        log4j2Metrics.bindTo(registry);

        // verify root logger
        Logger logger = loggerContext.getLogger(Log4j2MetricsTest.class);
        logger.info("Hello, world!");
        assertThat(registry.get("log4j2.events").tags("level", "info").counter().count()).isEqualTo(1);

        // verify other logger
        Logger logger2 = loggerContext.getLogger("com.test");
        logger2.info("Using other logger than root logger");
        assertThat(registry.get("log4j2.events").tags("level", "info").counter().count()).isEqualTo(2);

        log4j2Metrics.bindTo(registry2);

        logger.info("Hello, world!");
        assertThat(registry.get("log4j2.events").tags("level", "info").counter().count()).isEqualTo(3);
        assertThat(registry2.get("log4j2.events").tags("level", "info").counter().count()).isEqualTo(1);

        logger2.info("Using other logger than root logger");
        assertThat(registry.get("log4j2.events").tags("level", "info").counter().count()).isEqualTo(4);
        // this final check does not pass as the log event is not properly counted
        assertThat(registry2.get("log4j2.events").tags("level", "info").counter().count()).isEqualTo(2);
    }

The issue is the instanceof checks in Log4j2Metrics, it needs to check the correct instance of MetricsFilter to properly support registering multiple MeterRegistry (which is a very odd case anyway).

Originally posted by @pativa in #5818 (comment)