Fix bug #9511 (Can't select text in Extension Manager anymore) - Remove
no-focus from dialog root to allow text selection. Change scope of key
listener so tabbing continues to work without needing to reintroduce
tabIndex on the dialog, since that triggers Bootstrap-modal problems (#9196).

Also: add an extra error logging line so that failed updates always log some
error details to the console. (I think this case seemed to come up in a bug
a while back, but couldn't remember which one).
Merge pull request #9522 from adobe/pflynn/fix-extmgr-selection

Fix bug #9511 (Can't select text in Extension Manager anymore)