[llvm] [NFC][VPlan] Extract BTC-related tests into `vplan-based-stride-mv-btc.ll` (PR #214047)

[Andrei Elovikov via llvm-commits]

eas wrote:

I think https://github.com/llvm/llvm-project/pull/214838 should fix it.

https://github.com/llvm/llvm-project/pull/214047