Use spec-compatible logging trace context fields

[saisharan0103]

Fixes #4643.

The logging instrumentor was injecting trace context into LogRecord instances with OpenTelemetry-specific camelCase names: otelTraceID, otelSpanID, and otelTraceSampled. JSON formatters commonly serialize the raw record attributes, which meant the emitted fields did not match OpenTelemetry logging trace-context compatibility guidance.

This updates injection to populate record.trace_id, record.span_id, and record.trace_flags with lowercase hex IDs and W3C traceflags formatting. When no sampled span is active, trace_flags is set to 00; when a span context is present, it uses that context's W3C traceflags string.

DEFAULT_LOGGING_FORMAT and logging instrumentation docs now reference the snake_case record fields, while the default visible text output remains semantically equivalent except for reporting trace_flags instead of trace_sampled.

The logging tests were adjusted for the new attributes, with a regression assertion that a raw LogRecord dictionary exposes the spec-compatible JSON field names.

ruff check instrumentation/opentelemetry-instrumentation-logging/src/opentelemetry/instrumentation/logging/__init__.py instrumentation/opentelemetry-instrumentation-logging/src/opentelemetry/instrumentation/logging/constants.py instrumentation/opentelemetry-instrumentation-logging/tests/test_logging.py reports no new findings on the changed files.
Ran pytest -x locally with no new failures.

[linux-foundation-easycla]

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