[llvm] [AArch64][CostModel] Add NFC tests for extractelement cost (PR #108941)

[Sushant Gokhale via llvm-commits]

sushgokh wrote:

> Some of the half tests look like they should already be higher for fp16. It looks like you are hoping to adjust the cost of fmul lane operations?
They should be higher for non-fp16 since convert to float(32 bits) take place. The actual patch would try to reduce the cost of extracts from lane!=0



https://github.com/llvm/llvm-project/pull/108941