Replace ExactDsl by RaiseDsl

[CLOVIS-AI]

Hi! Sorry for not being very active the past few weeks. I'm currently catching up with everything that happened.

First, I'm impressed by how concise the result is. It's a single line longer than the current "use require in the constructor" idiom, and barely more verbose.

I've played a bit with the examples, and I'm not sure having a ExactDsl annotation is necessary. Since we decided to name the predicate function ensure for coherence with the rest of Arrow, I think we should use RaiseDsl instead.

Here is a simple example where I use both ensure. To me, this risks being confusing to users—after all, if IntelliJ highlights them differently, that means they do not relate to the same DSL, that's the entire point of DSL coloring—whereas we expect this to be completely legitimate code.

I don't think there is a valid use-case for nesting exact DSLs, so the annotation is only useful as documentation/coloration anyway. What do you think?