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;
     }

lib/Result.bux

@@ -31,6 +31,7 @@ module Std::Result {
     func Result_Unwrap<T, E>(r: Result<T, E>) -> T {
         if r.tag != Result_Ok {
             PrintLine("panic: unwrap on Err");
+            bux_exit(1);
         }
         return r.data.Ok_0;
     }
@@ -53,6 +54,7 @@ module Std::Result {
     func Result_UnwrapErr<T, E>(r: Result<T, E>) -> E {
         if r.tag != Result_Err {
             PrintLine("panic: unwrap_err on Ok");
+            bux_exit(1);
         }
         return r.data.Err_0;
     }