nim check: make error msgs less redundant

[timotheecour]

improve Example 3 from #16178

block:
  let a = bad5(1)

XDG_CONFIG_HOME= nim check --spellsuggest:0 --hints:off --filenames:canonical $timn_D/tests/nim/all/t12213.nim

before PR

tests/nim/all/t12213.nim(8, 13) Error: undeclared identifier: 'bad5'
tests/nim/all/t12213.nim(8, 17) Error: attempting to call routine: 'bad5'
  found 'bad5' [unknown declared in tests/nim/all/t12213.nim(8, 13)]
tests/nim/all/t12213.nim(8, 17) Error: attempting to call routine: 'bad5'
  found 'bad5' [unknown declared in tests/nim/all/t12213.nim(8, 13)]
tests/nim/all/t12213.nim(8, 17) Error: expression 'bad5' cannot be called
tests/nim/all/t12213.nim(8, 17) Error: expression '' has no type (or is ambiguous)
tests/nim/all/t12213.nim(8, 9) Error: 'let' symbol requires an initialization

after PR

tests/nim/all/t12213.nim(8, 13) Error: undeclared identifier: 'bad5'
tests/nim/all/t12213.nim(8, 17) Error: expression '' has no type (or is ambiguous)
tests/nim/all/t12213.nim(8, 9) Error: 'let' symbol requires an initialization

• add test for Trivial crash #12741 (since I'm changing related code)
• closes nim check: fix Example 2 from bug #16178 #17863 (because it's a more general fix)

note

if you have a concrete idea for how to avoid when defined(nimsuggest): ... I'm all ears, otherwise the change is good enough for now

future work

• use errorSubNode or newError(which uses the new nkError) instead of errorNode (which uses nkEmpty) so that we can also remove the 2nd and 3rd line; as explained in PR; this is a bigger change so can be done in future work (it's already hard enough because it interferes with nimsuggest)

[Araq]

if you have a concrete idea for how to avoid when defined(nimsuggest): ... I'm all ears, otherwise the change is good enough for now

I don't have an idea either but it's not "good enough for now", hacks like these live on for much too long in general and slow down development.