feat: use Prometheus metric family descriptors

[zeitlinger]

Draft PR for validating the Prometheus client_java opt-in descriptor API.

Depends on prometheus/client_java#2122, or a released client_java version containing
MetricFamilyDescriptor and the typed MultiCollector metadata opt-in.

Changes:

• Provide typed Prometheus metric family descriptors from MicrometerCollector
  without invoking scrape/sample callbacks.
• Use descriptors for counters, gauges, info metrics, summaries, histograms,
  distribution statistic _max families, and custom meter statistic families.
• Keep Micrometer's reserved suffix stripping behavior locally so existing name
  compatibility does not depend on client_java suffix-stripping internals.

Local validation against local client_java #2122 artifacts:

./gradlew --no-daemon -I /tmp/micrometer-prom-local.init.gradle \
  :micrometer-registry-prometheus:test

Result: passed.

[zeitlinger]

Closing this draft so the validation stays as two client_java PRs. The branch remains available for prometheus/client_java#2123 to test Micrometer's opt-in implementation.