Rollup merge of #141439 - compiler-errors:dyn-compatible-coerce, r=oli-obk

Deduplicate dyn compatibility violations due to coercion

Don't unnecessarily emit dyn compatibility violations due to coercion to a non-dyn-compatible target type.

For us to even have that target type, we would have had to write `dyn Trait` somewhere in source, and that would have led to us *already* emitting a dyn compatibility violation when checking that user written type is WF.

r? oli-obk

Author: jieyouxu