This PR improves error handling for PjRtPlugin and ComputationClient initialization. It provides better error messages and prevents repeated error reporting. A new test has been added for dynamic PjRtPlugin registration error.

Key Changes

• GetPjRtPlugin() function returns a FailedPreconditionError() if no PjRtPlugin was registered to the current PJRT_DEVICE with a better error message
• g_computation_client_initialized variable is only set if the ComputationClient is successfully initialized
  • Avoids showing the same error on _XLAC._prepare_to_exit() function
• Unwrapping the StatusOr<T> value in GetComputationClientOrDie() function by using GetValueOrThrow() function, instead of .value()
  • Avoids the error message prefix: Bad StatusOr access: INVALID_ARGUMENT
  • Centralizes error message with stacktraces in PR Dump C++ and Status propagation stacktraces. #9492
• Added test for checking the computation client initialization error due to unregistered dynamic PjRtPlugin