Add serial column to YAML form submissions.

Follow-up to #2802485: SubmissionID as a counter for submissions for each form

Problem/Motivation

YamlFormSubmission::sid is not an accurate counter for tracking submissions.

Proposed resolution

Add serial column to YAML form submissions.

Remaining tasks

• Add serial column to yamlform_submission table.
• Add next_serial to YamlFormSettings Form.
• Add code to set serial to \Drupal\yamlform\YamlFormSubmissionStorage::doSave
• Update YamlFormSubmission::label() to use serial.
• Update Results Download to use serial.
• Update Submission List builder to show serial column as #.
• Add hidden SID to Submission List builder.
• Update export by range
• Write update hook.

User interface changes

Serial value will be displayed instead of submission id (sid).

API changes

None

Data model changes

Serial (serial) column will be added to yamlform_submission table.

Development Notes

• Branch Name: 2806911-add-serial-column-to-submissions
• Commit message: Issue #2806911: Add serial column to YAML form submissions