Doc cleanup after FieldConfig

Can we also do https://www.drupal.org/node/2312093#comment-9164319 points 1 - 2 as well. Thanks.

+++ b/core/lib/Drupal/Core/Field/FieldConfigBase.php
@@ -32,7 +32,7 @@
-   * The name of the field attached to the bundle by this field.
+   * The machine name of the field attached to the bundle.

Can we use the same text than for FieldStorageConfig::$field_name ?

  /**
   * The field name.
   *
   * This is the name of the property under which the field values are placed in
   * an entity: $entity->{$field_name}. The maximum length is
   * Field:NAME_MAX_LENGTH.
   *
   * Example: body, field_main_image.
   *
   * @var string
   */

@andypost: no, I meant the other way around: do not touch FieldStorageConfig, and put in FieldConfigBase the same text that appears in FieldStorageConfig.

Sorry for letting this slide. #9 is good to go.
Thanks @andypost !

This looks like we have no test coverage then.

The

- $class::fieldSettingsFromConfigData($record['settings']);
+ $class::fieldSettingsToConfigData($record['settings']);

part got fixed (with the missing tests) in #2437785: FieldConfigStorageBase::mapToStorageRecord() calls the wrong field type method

This leaves just the doc fixes here. Reroll, and back to RTBC.

Documentation is not frozen in beta. Committed 374f838 and pushed to 8.0.x. Thanks!