Improve error reporting (#2376)

* Do not trim stack traces of exceptions with no stack trace

This prevents us from accidentally giving stack traces to exceptions
that don't have them and giving misleading messages telling users to use
--full-stacktrace when it won't actually do anything.

Also deprecate ChiselException.chiselStackTrace which is no longer being
used anywhere in this codebase.

* Add exception class for multiple-errors reported

New chisel3.internal.Errors replaces old anonymous class that would show
up as chisel3.internal.ErrorLog$$anon$1 in error messages.

* Add new option --throw-on-first-error

This tells Chisel not to aggregate recoverable errors but instead to
throw an exception on the first one. This gives a stack trace for users
who need it for debugging.