Description

Adds a shared _resolve_component() utility in _common.py that extracts the common pattern used by exporter factory functions for plugin loading.

Suggested by @lzchen in #5098.

The pattern

All three exporter factory functions (_create_span_exporter, _create_log_record_exporter, _create_push_metric_exporter) follow the same structure:

1. Iterate a registry of built-in names → call factory with config value
2. Check additional_properties for plugin names → load_entry_point(group, name)(**(config or {}))
3. Raise ConfigurationError if nothing matched

The utility

def _resolve_component(config, registry, entry_point_group, component_type):
    for name, factory in registry.items():
        value = getattr(config, name, None)
        if value is not None:
            return factory(value)
    if config.additional_properties:
        name, plugin_config = next(iter(config.additional_properties.items()))
        return load_entry_point(entry_point_group, name)(**(plugin_config or {}))
    raise ConfigurationError(f"No {component_type} type specified in config.")

Tests

5 tests covering: built-in resolution, plugin loading with config, plugin with empty config, no-component error, plugin-not-found error.

Draft — this PR adds the utility and tests only. The pending exporter PR (#5128) will be updated to use it once both land. The sampler, propagator, and resource detector have enough structural differences that they don't benefit from this utility.