[cling] Make cling::utils::Lookup::Named look into using directives

[devajithvs]

This Pull request:

Changes or fixes:

Checklist:

• [ ] tested changes locally
• [ ] updated the docs (if necessary)

This PR fixes https://github.com/root-project/root/issues/15407

[pcanal]

Is there a corresponding roottest PR enabling/adding test for this?

[github-actions[bot]]

Test Results

    14 files      14 suites   3d 10h 44m 0s :stopwatch:  2 697 tests  2 697 :white_check_mark: 0 :zzz: 0 :x: 35 511 runs  35 511 :white_check_mark: 0 :zzz: 0 :x:

Results for commit ca410ed8.

:recycle: This comment has been updated with latest results.

[devajithvs]

Is there a corresponding roottest PR enabling/adding test for this?

Added a cling test for this.

[hahnjo]

@devajithvs can you try enabling the test in roottest that was conditional on the fix: https://github.com/root-project/roottest/pull/1118 ?

[devajithvs]

Check running here: https://github.com/root-project/root/pull/16535 corresponding to https://github.com/root-project/roottest/pull/1194