internal/core/export: update error todos

The new evaluator ignores some fields for the doc tests
if there are errors. The most common case in the tests
is that it doesn't generate a bogus entry for a failed
dynamic field. This is good. In another case it is
arguably not the desired outcome, as the dynamic field
can be resolved in principle.

Update the diff comments accordingly.

Signed-off-by: Marcel van Lohuizen <mpvl@gmail.com>
Change-Id: I123e9d5e6f0c296bb993ce82bbce404eec8ece19
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1194466
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>

internal/core/export/testdata/main/dynamic.txtar

@@ -68,8 +68,12 @@ diff old new
  ["s-r"]
  ["s-q1"]
 -["s-q1" r1]
--- diff/out/todo/p1 --
-Missing lines.
+-- diff/out/todo/p3 --
+One missing entry is the result of the new evaluator not generating a
+bogus field for a failed dynamic field.
+The second one results from the fact that the new evaluator does not
+resolve `r1`, but rather propagates the error of the top-level node.
+This is probably okay.
 -- out/doc --
 []
 [x]

internal/core/export/testdata/main/issue2584.txtar

@@ -41,8 +41,9 @@ diff old new
 -[F2 _]
  [D]
  [L]
--- diff/out/todo/p1 --
-Missing line item.
+-- diff/doc/explanation --
+An incomplete dynamic field does not manifest itself as an invalid field
+in the new evaluator. This is probably for the better.
 -- out/doc --
 []
 [F1]