Auto merge of #123185 - scottmcm:more-typed-copy, r=compiler-errors

Remove my `scalar_copy_backend_type` optimization attempt

I added this back in rust-lang/rust#111999 , but I no longer think it's a good idea
- It had to get scaled back to only power-of-two things to not break a bunch of targets
- LLVM seems to be getting better at memcpy removal anyway
- Introducing vector instructions has seemed to sometimes (rust-lang/rust#115515 (comment)) make autovectorization worse

So this removes it from the codegen crates entirely, and instead just tries to use <https://doc.rust-lang.org/nightly/nightly-rustc/rustc_codegen_ssa/traits/builder/trait.BuilderMethods.html#method.typed_place_copy> instead of direct `memcpy` so things will still use load/store when a type isn't `OperandValue::Ref`.

Author: bors