feat: Update Logger#on_emit to create LogRecords

[kaylareopelle]

This PR creates a LogRecord class that is read/writeable to start with, and becomes read-only when it transitions to LogRecordData.

Additionally, it provides the SDK implementation of the Logs Bridge API Logger#on_emit method to emit LogRecords to the processing pipeline.

Relates to the following specs:

• Log Record Definition
• Readable Log Record
• Read Write Log Record
• Logger Operations: Emit a log record

Resolves: https://github.com/open-telemetry/opentelemetry-ruby/issues/1484