…ter (llvm#175913)

`dereferenceable(<n>)` with n being potentially zero can come up when
using an operand bundle with a variable size. Currently this implies
that the pointer is non-null, even though `[nullptr, nullptr)` is a
valid range in any programming language I'm aware of. This patch removes
this implication and updates the language reference to reflect that
`dereferenceable` with a zero argument is valid.

Based on Michael Maitland's previous work:
llvm#121222

This PR uses the existing recurrences code instead of introducing a
new pass just for CSA autovec. I've also made recipes that are more
generic.

Add handling for CTLS using the same method as in
llvm#174636.

Added tests to AArch64 and RISCV, but it seems that ARM is actually
resolving `llvm.arm.cls` to `clz`, so not tests added there.