impish: Emit sidebar-activated on when selection item in Desktop sidebar

[ids1024]

Fixes #195

[jacobgkau]

This is working to make the Desktop panels accessible in a narrow view. I'm seeing a couple of quirks.

• If I go into a page, then go back to the list, clicking the title again doesn't bring me back into that page:

Double-clicking does bring me back in, but that feels inconsistent since I didn't need to double-click the first time.

• The Appearance page's theme switcher is cut off:

It is horizontally scrollable, but seems like maybe it should break vertically instead of looking like this? (None of the other Desktop pages have to horizontally scroll.)

[ids1024]

If I go into a page, then go back to the list, clicking the title again doesn't bring me back into that page:

Good catch. Updated to use row-activated signal instead of row-selected, just like the Applications panel. Should work as expected now.

It is horizontally scrollable, but seems like maybe it should break vertically instead of looking like this?

Sounds good to me. See pop-os/theme-switcher#29 and pop-os/desktop-widget#73.

Since that's used as a shared library, that can be reviewed separately and doesn't block this PR, so this should be good now.

[jacobgkau]

After navigating into any of the Desktop sub-pages and then back to the topmost page list, accessing the Desktop section again goes straight to the General page instead of the Desktop list:

This does not happen with the Privacy section:

[jacobgkau]

Because this is an improvement over current behavior, at @jackpot51's request, I've opened #203 to track the remaining navigation issue and am approving this partial fix.