lib/be effects: Use DFA for fz -effects and avoid panic in mutate, fix #2293

[fridis]

Before this patch, the effects reported for HelloWorld.fz were useless:

   > ./build/bin/fz -effects build/tests/hello/HelloWorld.fz
  ((i32.infix ..).as_stream.#anonymous9.map_to_stream String).#anonymous1.as_array.m
  ((list String).as_stream.map_to_stream String).#anonymous1.as_array.m
  ((list i32).as_stream.map_to_stream String).#anonymous1.as_array.m
  ((list u8).as_stream.map_to_stream String).#anonymous1.as_array.m
  (i32.infix ..).as_stream.#anonymous9.as_array.m
  (list String).as_stream.as_array.m
  (list i32).as_stream.as_array.m
  (list u8).as_stream.as_array.m
  exit
  io.err
  io.out
  mutate
  panic

This patch fixes this by switching the effects backend used by fz -effects to use DFA instead for CFG, which give higher analysis accuracy and avoids the many ...as_array.m effects.

Then, effect.abortable was added as a feature that can be redefined to indicate that a given effect must not support abort. This helps removing the reported panic effect and consequently also io.err and exit.

Finally, the use of mutate effect was removed from exit (which is an effect already any may as well use set and list.as_array (which used mut in a local mutate instance, which made the local mutate instance useless). Also, the use of panic in mutate.check_and_replace was replaced by a precondition.

A minor cleanup in the code using a local mutate instance in Stream.as_array is also part of this patch.

fz -effects now supports -verbose=1, which will print the reason and a sample call chain why the reported effects are there, this facilitates understanding the results significantly. To reduce noise, verbose output of DFA was moved one verbosity level up.

The resulting output of fz -effects HelloWorld.fz now is

   > ./build/bin/fz -effects build/tests/hello/HelloWorld.fz
  io.out

While -verbose adds a nice explanation (plus some unrelated warnings that need to be fixed).

   > ./build/bin/fz -effects -verbose build/tests/hello/HelloWorld.fz
  []
  EFFECT type io.out default used is io.out
  program entry point
      |
      +- performs call HelloWorld => HelloWorld
        |
        +- performs call say a0=boxed(Const_String):Const_String => UNIT
  /home/fridi/fuzion/work/build/tests/hello/HelloWorld.fz:27:3:
    say "Hello World!"
  --^^^
          |
          +- performs call io.out => io.out embedded in io.out
  $FUZION/lib/say.fz:31:25:
  public say(s Any) => io.out.println s
  ------------------------^
            |
            +- performs call ((io.#type io).out.#type io.out).install_default => UNIT
  $FUZION/lib/io/out.fz:42:12:
    out.type.install_default
  -----------^
              |
              +- performs call io.out.default target=io.out => UNIT
  $FUZION/lib/io/out.fz:32:36:
      (io.out default_print_handler).default
  -----------------------------------^

  Elapsed time for phases: prep 66ms, fe 104ms, createMIR 1ms, me 91ms, ir 603ms, effectsCheck 104ms, be 256ms
  6 warnings.