ZeroVec::from_slice_or_alloc requires implementation of EqULE which shouldn't be needed as the method

[pandusonu2]

from_slice_or_allow trait shouldn't require EqULE, as only slice method requires that implementation, https://github.com/unicode-org/icu4x/blob/main/utils/zerovec/src/zerovec/mod.rs#L574

[sffc]

EqULE's sole purpose of existing is so that from_slice_or_alloc can work.

I want to move away from EqULE and from_slice_or_alloc in favor of const-constructing a ZeroSlice (#1935).

[Manishearth]

I'm not 100% sure if the const stuff would cover all use cases of from_slice_or_alloc fwiw. It does for our examples, but our examples don't cover everything

[sffc]

The use case for which EqULE/from_slice_or_alloc was introduced was having more readable, aligned data in code files, converted to ULE for runtime use. Const functions in #1935 solve this use case.

Last I looked around the code base at from_slice_or_alloc call sites, they mostly fit into this bucket. Any call sites that are for other cases may have separate solutions that are superior.