Release v2.21.0 (#332)

Minor release rounding up the 2.21.0 milestone.

- Setup makes sure there is a calendar to write to: it offers to create a local calendar or add a syncing account when the device has none, and lists switched-off calendars so they can be turned back on (#287).
- The month grid gives its days more room: smaller week numbers in a gutter measured from the widest number, less chip padding, tighter label tracking (#189, #190, #212, #213).
- A month day shows as many event chips as its week row has height for, instead of a flat three.
- Split view draws only the rows its month spans instead of padding to six (#162).
- Short events show their title in week and day view (#289).
- A fully zoomed-out timeline no longer scrolls by its rounding leftover (#290).
- Backup & restore has loading, failure and empty states instead of a blank page (#304).
- Untitled events and unnamed calendars use the translated placeholder instead of the hardcoded German one, which the calendar editor could also save into the calendar (#321, #329).

Plus the release commit: CHANGELOG section, versionName 2.21.0 / versionCode 22100, and the en-US 22100 changelog. Merging this to main triggers the release pipeline.

Closes #287
Closes #189
Closes #190
Closes #212
Closes #213
Closes #162
Closes #289
Closes #290
Closes #304
Closes #321
Closes #329

Co-authored-by: Jean-Luc Makiola <business@jeanlucmakiola.de>
Reviewed-on: https://codeberg.org/jlmakiola/calendula/pulls/332

app/build.gradle.kts

@@ -28,8 +28,8 @@ android {
         // which builds this version and then creates the matching vX.Y.Z tag +
         // release itself (versionCode is pinned to MAJOR*10000 + MINOR*100 +
         // PATCH from versionName, e.g. 2.7.2 -> 20702). See docs/RELEASING.md.
-        versionCode = 22004
-        versionName = "2.20.4"
+        versionCode = 22100
+        versionName = "2.21.0"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }