Don't report SC2218 when another definition's order is unknown

[Eljees]

Fixes #3509.

Minimal reproduction

The report says the case could not be shrunk below the 1069-line real library. It does reduce, and neither source nor bats is needed:

setup() { f() { true; }; }
f
f() { true; }

In t.sh line 2:
f
^-- SC2218 (error): This function is only defined later. Move the definition up.

The reported shape, with nothing sourced:

#!/usr/bin/env bats
setup() { f() { true; }; }
@test "a" {
  f
}
@test "b" {
  f() { true; }
}

Cause

checkUseBeforeDefinition warns when some definition post-dominates the call and no definition is post-dominated by it. Here there are two definitions: one inside setup's body, one at top level after the call. The top-level one satisfies the first guard; the one in setup satisfies neither relation, because nothing in the script visibly calls setup. So the check concludes "only defined later" while a definition whose order it cannot determine is sitting right there.

That definition may well have run. bats calls setup before every @test, and in an ordinary script a function can be reached through a trap, an indirect call, or a sourcing parent. SC2218 is an error, whereas SC2329 ("This function is never invoked") is only an info, hedged with "or ignored if invoked indirectly", for exactly that reason.

Change

Require every definition to come after the call rather than just one. The second guard stays as it is: inside a loop a definition can both post-dominate the call and be post-dominated by it.

The true positives are unaffected: prop_checkUseBeforeDefinition1 and 5 still fire, 2, 3, 4 and 6 still don't. Two props are added for the two shapes above. Both fail on master and pass with the change, and cabal test is green.

The reporter's original case, with their betteropts.sh, goes from the SC2218 above to exit 0.