event-editor: Create GcalTimeChooserRow

Create a new GcalTimeChooserRow widget from AdwEntryRow that parses the
entry into a time, or lets the user pick a time from a popover.

[feaneron] Improved code style, reworked regex management.

src/gui/event-editor/meson.build

@@ -18,5 +18,6 @@ sources += files(
   'gcal-reminders-section.c',
   'gcal-schedule-section.c',
   'gcal-summary-section.c',
+  'gcal-time-chooser-row.c',
   'gcal-time-selector.c',
 )