fi-0018: Ordinals must start at 1 {:#fi-0018}

Neither table nor union member ordinal values are allowed to be 0:

{% include “docs/reference/fidl/language/error-catalog/label/_bad.md” %}

{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/bad/fi-0018.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}

Instead, numbering should start from 1:

{% include “docs/reference/fidl/language/error-catalog/label/_good.md” %}

{% includecode gerrit_repo="fuchsia/fuchsia" gerrit_path="tools/fidl/fidlc/tests/fidl/good/fi-0018.test.fidl" exclude_regexp="\/\/ (Copyright 20|Use of|found in).*" %}