Fix the ordering for future talks

Rather than the custom event sorting plugin being based on the `created`
value, this change adds a new `field_event_date` field to the talk node
type and uses this for the sorting instead.

This commit also adds a new `TalkDateUpdater` service that extracts
either the next event date if there is a future date, or the last past
event date if there is no future date, from `field_events` for each talk
and saves it into the event date field.

For consistency, and to ensure that the results are ordered correctly,
the talk date updater converts the date from a date string (e.g.
`2020-08-24`) into a UNIX timestamp, and the timestamp is saved in the
event date field. This can be changed at a later date if needed.

The talks view has been updated to use the updated sort plugin, and the
existing tests have been updated to use the new field.

References #204

config/default/core.entity_form_display.node.talk.default.yml

@@ -4,6 +4,7 @@ status: true
 dependencies:
   config:
     - field.field.node.talk.body
+    - field.field.node.talk.field_event_date
     - field.field.node.talk.field_events
     - field.field.node.talk.field_excerpt
     - field.field.node.talk.field_slides
@@ -143,4 +144,5 @@ content:
     region: content
     settings: {  }
     third_party_settings: {  }
-hidden: {  }
+hidden:
+  field_event_date: true

config/default/core.entity_view_display.node.talk.default.yml

@@ -4,6 +4,7 @@ status: true
 dependencies:
   config:
     - field.field.node.talk.body
+    - field.field.node.talk.field_event_date
     - field.field.node.talk.field_events
     - field.field.node.talk.field_excerpt
     - field.field.node.talk.field_slides
@@ -66,4 +67,5 @@ content:
     settings: {  }
     third_party_settings: {  }
 hidden:
+  field_event_date: true
   field_excerpt: true

config/default/core.entity_view_display.node.talk.teaser.yml

@@ -5,6 +5,7 @@ dependencies:
   config:
     - core.entity_view_mode.node.teaser
     - field.field.node.talk.body
+    - field.field.node.talk.field_event_date
     - field.field.node.talk.field_events
     - field.field.node.talk.field_excerpt
     - field.field.node.talk.field_slides
@@ -32,6 +33,7 @@ content:
     third_party_settings: {  }
 hidden:
   body: true
+  field_event_date: true
   field_events: true
   field_slides: true
   field_type: true

config/default/field.field.node.talk.field_event_date.yml

@@ -0,0 +1,23 @@
+uuid: 5c54e34a-4e53-4e70-b621-1d40953385cd
+langcode: en
+status: true
+dependencies:
+  config:
+    - field.storage.node.field_event_date
+    - node.type.talk
+id: node.talk.field_event_date
+field_name: field_event_date
+entity_type: node
+bundle: talk
+label: 'Next event date'
+description: ''
+required: false
+translatable: false
+default_value: {  }
+default_value_callback: ''
+settings:
+  min: 0
+  max: null
+  prefix: ''
+  suffix: ''
+field_type: integer

config/default/field.storage.node.field_event_date.yml

@@ -0,0 +1,20 @@
+uuid: 86aec221-e3cb-4da3-90b5-522b661c6313
+langcode: en
+status: true
+dependencies:
+  module:
+    - node
+id: node.field_event_date
+field_name: field_event_date
+entity_type: node
+type: integer
+settings:
+  unsigned: false
+  size: normal
+module: core
+locked: false
+cardinality: 1
+translatable: true
+indexes: {  }
+persist_with_no_fields: false
+custom_storage: false

config/default/views.view.talks.yml

@@ -144,7 +144,7 @@ display:
       sorts:
         event_sort:
           id: event_sort
-          table: node_field_data
+          table: node__field_event_date
           field: event_sort
           relationship: none
           group_type: group
@@ -154,7 +154,6 @@ display:
           expose:
             label: ''
           granularity: second
-          entity_type: node
           plugin_id: event_sort
       title: Talks
       header: {  }