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/doWhileEarlyContinue.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 fun x(): Boolean { return true }
 
 fun y(): Boolean { return false }