gui: Port to Blueprint

This was mostly done with `blueprint-compiler port`.

Since Blueprint doesn't know about custom templates, I had to manually change some values from strings to literals.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/567>

src/gui/event-editor/meson.build

@@ -1,9 +1,37 @@
 calendar_incs +=  include_directories('.')
 
+blueprints = custom_target(
+  'blueprints',
+  input: files(
+    'gcal-alarm-row.blp',
+    'gcal-date-chooser-row.blp',
+    'gcal-date-selector.blp',
+    'gcal-date-time-chooser.blp',
+    'gcal-event-editor-dialog.blp',
+    'gcal-multi-choice.blp',
+    'gcal-notes-section.blp',
+    'gcal-reminders-section.blp',
+    'gcal-schedule-section.blp',
+    'gcal-summary-section.blp',
+    'gcal-time-chooser-row.blp',
+    'gcal-time-zone-dialog-row.blp',
+    'gcal-time-zone-dialog.blp',
+  ),
+  output: '.',
+  command: [
+    find_program('blueprint-compiler'),
+    'batch-compile',
+    '@OUTPUT@',
+    '@CURRENT_SOURCE_DIR@',
+    '@INPUT@',
+  ],
+)
+
 built_sources += gnome.compile_resources(
   'event-editor-resources',
   'event-editor.gresource.xml',
   c_name: 'event_editor',
+  dependencies: blueprints,
 )
 
 sources += files(