Enforce RTLIL Wire/Const limit size of 2^24

[lethalbit]

This commit adds asserts to the RTLIL parser to ensure that a wire definition is no more than 2^24 bits wide, as well as that RTLIL Consts can not have a negative width nor be wider than 2^24 bits.

This addresses #1206 and #3317

[Ravenslofty]

I think the correct thing to use here is log_error rather than throwing an exception. I doubt any code is going to catch it anyway.

[lethalbit]

Possibly, I'll see how it feels with log_error, I also need to test to see how things like memories interact with the changes, although all the tests pass we don't have any that would directly exercise this code that I know of, so more work absolutely needs to be done on it.

[nakengelhardt]

Looking at the surrounding code, +1 on log_error.

[nakengelhardt]

We need to test where large consts may be created:

• memory initialization
• FSM transition tables
• others?

[arcturusannamalai]

it maybe better to use a constexpr defined in rtlil.h instead of repeating the magic number everywhere; my 2-cents

[whitequark]

This should probably be a log_assert rather than log_error since this case isn't supposed to ever happen.