Convert theme_system_themes_page() to Twig

Split from the system module twig conversion meta.

typo fix.

4: 2151119-4-twig-theme_system_themes_page.patch queued for re-testing.

Re-roll and leave the form alter were it was.

Reroll of path in #8.

Here is the profiling of the patch in #10.

=== 8.x..8.x compared (52e3e4975b356..52e3e4dce8a32):

ct  : 56,131|56,131|0|0.0%
wt  : 350,578|351,401|823|0.2%
cpu : 334,639|335,689|1,050|0.3%
mu  : 15,056,104|15,056,104|0|0.0%
pmu : 15,183,712|15,183,712|0|0.0%


=== 8.x..theme-system-twig compared (52e3e4975b356..52e3e5149d9ad):

ct  : 56,131|56,553|422|0.8%
wt  : 350,578|351,361|783|0.2%
cpu : 334,639|335,033|394|0.1%
mu  : 15,056,104|15,104,792|48,688|0.3%
pmu : 15,183,712|15,234,608|50,896|0.3%

I've also quickly checked visually and the markup of admin/appearance . Seems to be fine but I did not check for the case where a theme doesn't have a screenshot.

Fixed comments standards in the previous patch.

Thanks @Cottser, for the answer.
Oops, we really missed it. Added it back ;)

Did some manual testing and everything works as expected.

The patch looks good and the markup also doesn't have any significant difference.

+++ b/core/modules/system/templates/system-themes-page.html.twig
@@ -0,0 +1,61 @@
+            {# Display operation links if the theme is compatible. #}
+            {% if not theme.incompatible %}
+              {{ theme.operations }}
+            {% else %}
+              <div class="incompatible">{{ theme.incompatible }}</div>
+            {% endif %}

The double negatives are hard to read in code. Just swap the blocks and remove 'not'.

Otherwise I like these changes alot:)

Thanks for identifying an easy new contributor task! Here is the new patch and interdiff. Setting to needs review.

Back to RTBC, did another markup review and it's looking good. Attached are the before and after markup and the normalized versions for the screenshot and easier review.

Shoot. Really sorry to say, but this one no longer applies. Can we get a quick re-roll?

Quick re-roll as requested:)

Actually, sorry.. #22 applied just fine with patch -p1.

Committed and pushed to 8.x. Thanks!