Add accessible check for import usage

[som-snytt]

Fixes #23347

The code for deciding whether a selector is used to import a symbol was missing a check for accessibility (importability).

3.6.4 doesn't warn, so it would be nice to know why it excludes the member. The algorithm is different but the code for choosing import selectors is similar. 3.7.0 also doesn't warn, but no change stands out as a culprit. Possibly the selector was spuriously excluded (by result caching in 3.7.0).