Advanced Custom Fields Pro 6.2.9

* New - Added "Preview Size" and "Return Format" settings to the Gallery field.
* Tweak - Improved metabox styling for Gutenberg.
* Tweak - Changed default "Preview Size" to medium for the Image field.
* Fix - Fixed bug in media modal causing the primary button text to disappear after editing an image.
* Fix - Fixed bug preventing the TinyMCE Advanced plugin from adding `< p >` tags.
* Fix - Fixed bug where HTML choices were not visible in conditional logic dropdown.
* Fix - Fixed bug causing incorrect order of imported/synced flexible content sub fields.
* i18n - Updated German translation thanks to Ralf Koller.
* i18n - Updated Persian translation thanks to Majix.

* New - Added ACF Blocks feature for ACF PRO.
* Fix - Fixed bug causing duplicate "save metabox" AJAX requests in the Gutenberg editor.
* Fix - Fixed bug causing incorrect Repeater field value order in AJAX requests.
* Dev - Added JS filter `'relationship_ajax_data'` to customize Relationship field AJAX data.
* Dev - Added `$field_group` parameter to `'acf/location/match_rule'` filter.
* Dev - Bumped minimum supported PHP version to 5.4.0.
* Dev - Bumped minimum supported WP version to 4.7.0.
* i18n - Updated German translation thanks to Ralf Koller.
* i18n - Updated Portuguese language thanks to Pedro Mendonça.

Fix - Fixed bug causing issues with registered fields during `switch_to_blog()`.
Fix - Fixed bug preventing sub fields from being reused across multiple parents.
Fix - Fixed bug causing the `get_sub_field()` function to fail if a tab field exists with the same name as the selected field.
Fix - Fixed bug corrupting field settings since WP 5.1 when instructions contain `< a target="" >`.
Fix - Fixed bug in Gutenberg where custom metabox location (acf_after_title) did not show on initial page load.
Fix - Fixed bug causing issues when importing/syncing multiple field groups which contain a clone field.
Fix - Fixed bug preventing the AMP plugin preview from working.
Dev - Added new 'pre' filters to get, update and delete meta functions.
i18n - Update Turkish translation thanks to Emre Erkan.