[llvm] [LV][EVL] Support cast instruction with EVL-vectorization (PR #108351)

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LiqinWeng wrote:

> Apologies for the late reply since I just finished a long vacation. I'm happy to see that someone else is also contributing to EVL vectorization. :)

Pls give me 'LGTM'  :)~~~

https://github.com/llvm/llvm-project/pull/108351