fix modular pipeline class resolution for families outside the auto-pipeline mappings (#14736)

* resolve modular pipeline classes for families outside the auto-pipeline mappings and fail clearly without blocks

* test modular class resolution outside the auto-pipeline mappings

* register ltx in the auto video mappings instead of resolving by pipeline folder

* drop the unreachable workflow check and rename the resolution test

* move the resolution asserts into the fallback test

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Co-authored-by: YiYi Xu <yixu310@gmail.com>