Update Internal.valid_attributes for reuse with log records

[kaylareopelle]

There's a lot of duplication among the tracing SDK and the logs SDK. One of the areas of duplication is with LogRecord#validate_attributes. This is very similar to the code in Internal.valid_attributes.

Once the logs SDK is stable and we're ready to bring it into the main SDK gem, refactor Internal.valid_attributes for use with both signals. Depending on the timing, this may also be helpful for metric attribute validation as well.

This issue originated from this comment: https://github.com/open-telemetry/opentelemetry-ruby/pull/1696/files#r1759599051