ENH Refactor TagField from class to functional component

[emteknetnz]

Issue #336

Can test with the following:

// app/src/BlogPostAdmin.php

use SilverStripe\Admin\ModelAdmin;

class BlogPostAdmin extends ModelAdmin
{
    private static string $url_segment = 'blog-post-admin';
    private static string $menu_title = 'Blog Post Admin';
    private static array $managed_models = [
        BlogPost::class,
        BlogTag::class,
    ];
}

// app/src/BlogPost.php

use SilverStripe\Forms\FieldList;
use SilverStripe\ORM\DataObject;
use SilverStripe\TagField\TagField;

class BlogPost extends DataObject
{
    private static string $table_name = 'BlogPost';
    private static string $singular_name = 'Blog Post';
    private static string $plural_name = 'Blog Posts';

    private static array $db = [
        'Title' => 'Varchar(255)',
        'Content' => 'Text',
    ];

    private static array $many_many = [
        'BlogTags' => BlogTag::class
    ];

    public function getCMSFields(): FieldList
    {
        $fields = parent::getCMSFields();
        $field = TagField::create(
            'BlogTags',
            'Blog Tags',
            BlogTag::get(),
            $this->BlogTags()
        )
            ->setShouldLazyLoad(true)
            ->setCanCreate(true);
        $fields->addFieldToTab('Root.Main', $field);
        return $fields;
    }
}

// app/src/BlogTag.php

use SilverStripe\ORM\DataObject;

class BlogTag extends DataObject
{
    private static string $table_name = 'BlogTag';

    private static array $db = [
        'Title' => 'Varchar(200)',
    ];

    private static array $belongs_many_many = [
        'BlogPosts' => BlogPost::class
    ];

    private static string $singular_name = 'Blog Tag';
    private static string $plural_name = 'Blog Tags';

    public function requireDefaultRecords(): void
    {
        parent::requireDefaultRecords();
        $tags = [
            'Lorem Ipsum',
            'Dolor Sit Amet',
            'Consectetur Adipiscing',
            'Elit Sed Do',
            'Eiusmod Tempor',
            'Incididunt Ut Labore',
            'Et Dolore Magna Aliqua',
            'Ut Enim Ad Minim',
        ];
        foreach ($tags as $title) {
            if (!self::get()->filter('Title', $title)->exists()) {
                $tag = self::create();
                $tag->Title = $title;
                $tag->write();
            }
        }
    }
}

[GuySartorelli]

Seems to work as expected locally - just some variable naming to square away and possible changes to usage of callback hook as below.

[GuySartorelli]

Just the one thing now

[GuySartorelli]

LGTM