sink parameter inference for types that have destructors (#13544)

* ensure capitalize doesn't take an inferred sink parameter

* sink parameter inference: first version, for now disabled. Changed that sink parameters can be consumed multiple times in order to adhere to our spec.

* sink inference can now be disabled with .nosinks; sometimes for proc type interop this is required

* fixes yet another critical DFA bug

* better implementation that also understands if expressions etc

* document sink parameter inference and allow for global disabling

lib/pure/unicode.nim

@@ -701,7 +701,7 @@ proc capitalize*(s: string): string {.noSideEffect, procvar,
     doAssert capitalize("βeta") == "Βeta"
 
   if len(s) == 0:
-    return s
+    return ""
   var
     rune: Rune
     i = 0