arrow

GH-43787: [C++] Register the new Opaque extension type by default (#43788)

This is to resolve #43787

> The Opaque extension type implementation for C++ (plus python bindings) was added in https://github.com/apache/arrow/pull/43458, but it was not registered by default, which we should do for canonical extension types (see https://github.com/apache/arrow/pull/43458#issuecomment-2302551404)

Additionally, this adds `bool8` extension type builds with `ARROW_JSON=false` as discussed [here](https://github.com/apache/arrow/commit/525881987d0b9b4f464c3e3593a9a7b4e3c767d0#r145613657)

### Rationale for this change

Canonical types should be registered by default if possible (except e.g. if they can't be compiled due to `ARROW_JSON=false`).

### What changes are included in this PR?

This adds default registration for `opaque`, changes when `bool8` is built and moves all canonical tests under the same test target.

### Are these changes tested?

Changes are tested by previously existing tests.

### Are there any user-facing changes?

`opaue` will now be registered by default and `bool8` will be present in case `ARROW_JSON=false` at build time.
* GitHub Issue: #43787

Authored-by: Rok Mihevc <rok@mihevc.org>
Signed-off-by: Rok Mihevc <rok@mihevc.org>