ENG-5956 sqlcmd error handling improvements

Restructured try/catch blocks and a few throws especially in the area of exec parameter validation, mainly to allow more consistent options for stopping immediately on error or soldiering on, and returning a proper exit code on actual errors. But also a little bit just to eliminate redundant code.

Did NOT address the clumsy code sharing between interactive and batch modes (source of batch mode bugs and lots of unwanted complexity) 
or the lack of code sharing between batch mode and the almost-yet-should-be-more identical "script file read" mode.

Did not address needless complexity and compute costs in the LIST commands, in procedure identification, and in literal string handling.
An argument could be made that (at least most of the time? -- for most types?) argument values should just be sent as strings and the validation and conversion left to the ProcedureRunner parameter processing -- this would risk losing the nice "yes/no/true/false" handling, I'm not sure what else. That could greatly simplify SQLCommand.java.