Fix issue with hoisting and copy prop interaction (#85493)

Fix issue with hoisting and copy prop interaction (#85493)

* Fix issue with hoisting and copy prop interaction

After hoisting creates a tree copy, it morphs it. That morph might
lose the value numbers on LCL_VAR uses, but leave the SSA numbers.
Copy prop was assuming that such a use had a VN. Instead, check this
dynamically instead of asserting.

Fixes #84619

* Further optimize cast in fgOptimizeCastOnStore()

If we optimize the cast, call `fgOptimizeCast` to see if it can be
optimized further.

* Add regression test

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