Fix comparison check for field changes

Problem/Motivation

When loose comparison (++) is used, PHP changes casts values to different types to see if they match. This means numeric strings may be considered equal even if their string values are different.

Steps to reproduce

1. Set a field value to 1.
2. Try to change it to +1.
3. Drupal sees the field as unchanged.

Proposed resolution

Use exact comparison to check if field has changed.

Remaining tasks

1. Create merge request.
2. Create tests.
3. Review.
4. Merge.

User interface changes

None.

Introduced terminology

None.

API changes

None.

Data model changes

None.

Release notes snippet