FIR DFA: make continue jump to condition entry, not loop entry

It's also not a backwards jump in do-while, unless it's in the loop's
condition, which is a stupid "feature" IMO. As you can probably tell
from the comments added in this commit.

compiler/testData/diagnostics/tests/smartCasts/loops/nestedDoWhileWithLongContinue.fir.kt

@@ -5,10 +5,10 @@ public fun foo(p: String?, r: String?): Int {
         do {
             p!!.length
             if (!x()) continue@outer
-        } while (r == null)  
+        } while (r == null)
     } while (!x())
     // Auto cast NOT possible due to long continue
-    r.length
+    r<!UNSAFE_CALL!>.<!>length
     // Auto cast possible
     return p.length
 }