ApplicationLongGaugeBuilder missing buildObserver() bridge method

[breedx-splk]

The interface has a default method, which is probably why this didn't show up.

To reproduce this problem:

Meter testMeter = GlobalOpenTelemetry.getMeter("test");
ObservableLongMeasurement b = testMeter.gaugeBuilder("b")
        .ofLongs().buildObserver();

The result is a noop gauge.

We need to implement the bridge method so that users won't always get the noop implementation.

[breedx-splk]

Looks like this is also true for ApplicationDoubleGaugeBuilder as well.