Better diagnostics for compile-time errors

[Iltotore]

When a compile-time error occurs due to the value to refine not being evaluable at compile-time, the message can be quite confusing for newcomers. It would be useful to detect some easy mistakes (such as forgetting an inline) when such error occurs and provide a better message accordingly.

Example:

val notInlined: Int = 5
val pos: Int :| Positive = notInlined //`notInlined` is not a non-inlined variable. You need to make it `inline` in order to check it at compile-time etc.

Errors worth detecting are:

• Condition not evaluable
• Value of a non evaluable type (because lack of FromExpr). This will be especially useful for future versions. See Allow constraints for non-primitive types to be evaluable at compile-time #147
• Value not evaluable due to a variable/method not being inlined
• Value not evaluable for a miscellaneous