fix: is-operator, try with generic Result, Unwrap exits on panic

Desugar `is` to tag/value equality in bootstrap and selfhost so LIR
no longer drops hIs as false. Resolve monomorphized Result/Option type
names for `?` (_Tag/_Data). Call bux_exit(1) after Unwrap panic messages.
Add is_operator example and document follow-up fixes.

lib/Option.bux

@@ -29,6 +29,7 @@ module Std::Option {
     func Option_Unwrap<T>(o: Option<T>) -> T {
         if o.tag != Option_Some {
             PrintLine("panic: unwrap on None");
+            bux_exit(1);
         }
         return o.data.Some_0;
     }