This closes#10146.
Because of cibernox/ember-power-select#1203, which documents
the current impossibility of attaching test selectors to a
PowerSelect invocation, this uses test selectors on parent
containers instead, occasionally adding wrappers when needed.
I chose to leave the existing test selectors in the hopes that
we can return to using them eventually, but I could easily
remove them if it seems like extra noise now.
Presumably for the same reason, @class no longer works, so
this adjusts the scoping of global search CSS to preserve the style
of the search control.
I also included an update to the latest version of
ember-test-selectors, since we were far behind and I tried
that before finding the aforelinked issue.
Finally, this replaces ember-cli-uglify with ember-cli-terser to address
production build failures as described at ember-cli/ember-cli#9290.
This introduces ember-a11y-testing to acceptance tests via a helper
wrapper that allows us to globally ignore rules that we can address
separately. It also adds fixes for the aXe rules that were failing.
This includes fixes for newer template lint rules that came along with
updating that dependency, which was necessary to be able to use
the no-curly-component-invocation rule. It also updates some curly
invocations that I missed in #8075.
