Introduce DeclarativeConfigResult to eliminate reflection in IncubatingUtil

[zeitlinger]

Context

Builds on top of open-telemetry#8242.

The sharedState field reflection in IncubatingUtil introduced in open-telemetry#8242 is a regression — it accesses a private internal field of SdkMeterProvider to extract Resource, which is fragile and goes against the direction discussed in open-telemetry#7292.

Change

Introduce DeclarativeConfigResult (in fileconfig.internal — not public API) as the return type of DeclarativeConfiguration.create(). It carries both the configured SDK and Resource as first-class values, so IncubatingUtil can read them directly with no reflection.

Target module structure per open-telemetry#7292:

common (ComponentLoader)
  └── autoconfigure-spi (ConfigProperties, Ordered, ComponentProvider, AutoConfigureListener)
        └── sdk-config (OpenTelemetryConfigurationModel, SdkConfigProvider,
        |               DeclarativeConfiguration.create(), DeclarativeConfigContext,
        |               DeclarativeConfigurationProvider SPI,
        |               DeclarativeConfigurationCustomizer SPI)
              ├── sdk (OpenTelemetrySdk)
              ├── sdk-config-parse (DeclarativeConfiguration.parse(), Jackson/YAML)
              └── autoconfigure (invokes parse+create when OTEL_EXPERIMENTAL_CONFIG_FILE set)

DeclarativeConfigResult is the natural precursor to the result type that create() will need in the target architecture (where sdk-config cannot depend on sdk and must return individual providers + resource rather than an assembled OpenTelemetrySdk).

Does this match the target picture in open-telemetry#7292?