Twenty Seventeen: role="complementary" are missing labels

[sami.keijonen]

From the quidelines:

If a particular role appears more than once on a page, you should provide an ARIA label for that role

We do this already for <navigation> but not for <aside>. Just like navigation there can be several <aside role="complementary"> in the theme and we should provide labels for them. Otherwise screen readers would announce 2 "complementary" regions without knowing the separation of them

​https://cloudup.com/cOjsuxTbf1E

I propose that we add labels to <aside> with the same as widget names:

1. Blog Sidebar
2. Footer 1
3. Footer 2

[sami.keijonen]

Added a patch and finding good wording is super hard in this case because you don't know what kind of widgets there will be.

For now I added

1. Blog Sidebar
2. Footer

Here is screenshot after the patch.

[SergeyBiryukov]

In 41687:

Twenty Seventeen: Add missing labels for <aside role="complementary"> widget areas.

Props sami.keijonen.
Fixes #42056.