Non-macro alternative to `Ash.Query.filter`

All `Ash.Query` modifications - `select`, `sort`, `limit`, `offset`, `build` and so on - are usual methods. Except one, the most used - `filter` - it is a macro. So it needs a require statement to be used. Which is a little bit annoying when you want to add a simple filter and only once in a file... I just go for `build(filter:)` combo in that case.

Would be convenient to have non-macro variant of `filter` exposed (which is `do_filter`). Maybe under name `where`?

In small discussion on Discord the following proposal was made: add `where` in Ash 3.1 (because there are too many things already in Ash 3 and it is too late to change `filter` to non-macro method even though it is desirable) and make it a primary way to add filters to queries in docs, then in Ash 4 deprecate `filter`.

Start by reading the Ash.Query.filter macro, its do_filter implementation, and the existing build(filter:) path mentioned in the issue. Check how query modifiers are exposed and documented; done means an agreed non-macro API and compatible documentation/deprecation plan for the stated Ash 3.1/Ash 4 transition.

Written by the indexing model from the issue text.