[llvm] [CodeGen][LLT] Add isFixedVector and isScalableVector (PR #71713)

[Michael Maitland via llvm-commits]

michaelmaitland wrote:

> I'd consider that a bug in the first place. It shouldn't assert

The docstring specifies a precondition that the LLT is a vector type. So by asserting, it is checking that precondition, which does not seem like a bug. However, I do wonder if we can drop this precondition so we can drop the assert.

https://github.com/llvm/llvm-project/pull/71713