Support `three` methods of the log `concatenation` in the `structured logging framework`

Allow log syntax like

• 1.log"... MDC(...) $normal_variables ..."

  log"Driver terminated with exit code ${MDC(EXIT_CODE, exitCode)}! Shutting down. $remoteAddress"
  

• 2.s"... $normal_variables ..." ++ log"... MDC(...) ..."

  log"Driver terminated with exit code ${MDC(EXIT_CODE, exitCode)}! Shutting down." ++ s"$remoteAddress"
  

• 3.log"... MDC(...) ..." ++ s"... $normal_variables ..."

  s"$remoteAddress" ++ log"Driver terminated with exit code ${MDC(EXIT_CODE, exitCode)}! Shutting down."