refactor(developer): kmc-model to use CompilerEvent

Replaces the existing error reporting in kmc-model with CompilerEvent
style messages. Some of the existing error reporting was kinda nice, but
consistency trumps pretty here.

One downside at present is the global filename and line variables in the
model-compiler-errors.ts unit. This is fragile, and should probably be
refactored further in the future.

Where it made sense, I converted various throws into ModelCompilerError
instances. If it appeared to be an internal error, I left it as-is, but
the external API interfaces wrap all unknown exceptions and convert them
into a compiler error message, so these APIs (compileModel and
loadFromFilename) now have a guarantee that they will never throw.

At this point, all of the error messages in the model compiler are
unrecoverable -- they will halt the compile entirely. However, the
pathway is there to support recoverable errors through the normal
callbacks.reportMessage mechanisms.

The message-counting mechanism is currently missing from this, as it
belongs in the API consumer, rather than in the low-level reporting
infrastructure. This means that models with large numbers of warnings
are going to generate scads of messages for now.

Note that the _users_ of CompilerCallbacks are subject to change in the
future, once we have all the compilers using the callbacks.