Refactor D7 FieldInstance source plugin and other field instance related source plugins

Self-assigning for review.

Assigning to myself for review this week.

I really like how this is shaping up. Some minor points noted.

1. +++ b/core/modules/field/migration_templates/d7_field_instance.yml
   @@ -19,15 +19,15 @@ process:
   -      - instance_settings
   -      - widget_settings
   -      - field_settings
   +      - settings
   +      - widget
   +      - field_definition
   ...
          - default_value
   -      - widget_settings
   +      - widget
   

   This is a BC break that gets exposed to users of migrate_drupal. If someone starts migrating their site on 8.3, then in 2 months updates the site to 8.4, the field instance migrations are going to die a horrible death. We can either address this in a CR or keep a BC shim in place. Perhaps we can go with a CR since migrate_drupal is still experimental and the needed changes for the scenarios just mentioned are fairly minor.

2. +++ b/core/modules/text/src/Plugin/migrate/cckfield/TextField.php
   @@ -43,7 +43,9 @@ public function getFieldFormatterMap() {
   +    $widget_type = isset($field_info['widget_type']) ? $field_info['widget_type'] : $field_info['widget']['type'];
   

   Are we sure we need this? I don't see where we are pulling 'widget_type'.

Chatted about this in IRC and we are OK with breaking BC and the necessary updates for the field_instance yml file. But that means we need a CR.

+++ b/core/modules/field/src/Plugin/migrate/process/d7/FieldInstanceSettings.php
--- a/core/modules/field/src/Plugin/migrate/source/d7/FieldInstance.php
+++ b/core/modules/field/src/Plugin/migrate/source/d7/FieldInstance.php

Mark this @internal.

Going to work on a draft CR. Patch in #14 is looking good.

@maxocub in IRC: FieldInstancePerFormDisplay.php FieldInstancePerViewMode.php ViewMode.php all should maybe extend FieldInstance where possible

Back to NW.

I'm gonna be 'that guy' - here are a few coding standards corrections.

Going to review this.

One small question. Otherwise, this looks good to go. I also added a quick 8.5 test, just to make sure nothing fishing is going on here.

+++ b/core/modules/field/src/Plugin/migrate/process/d7/FieldInstanceDefaults.php
@@ -19,6 +19,11 @@ class FieldInstanceDefaults extends ProcessPluginBase {
+    if ($widget_type == 'email_textfield' && $default_value) {
+      $default_value[0]['value'] = $default_value[0]['email'];

This seems odd. Can we add a comment why this is needed?

All my concerns addressed. LGTM and unblock our critical.

Un assigning

In #2842222-107: D7 Plain text fields incorrectly migrated to D8 as Text (formatted), that critical issue was marked postponed on this issue. If this issue is a hard blocker, it needs to be critical itself.

Promoting this one to critical, at least for now so that is visible and can be evaluated.

This is a hard blocker. So bumping priority is a good suggestion.

Committed/pushed to 8.5.x and cherry-picked to 8.4.x. Thanks!