[llvm] [CostModel] Estimate the codesize cost of switch (PR #163569)

[Hongyu Chen via llvm-commits]

XChy wrote:

> Why did you change this from the implementation that queries the load etc costs to one that doesn't?

Because it's more complicated to query these costs in TTIImpl, and I expected the code size cost of most targets to be consistent, I tried to simplify this code. Will change it back to the general form with queries if that's better.

https://github.com/llvm/llvm-project/pull/163569