Use get_admin_display_title in PageChooserPanel

[SaptakS]

Should fix #5726 . @gasman This should fix the title of the page only in the PageChooserPanel. Do you think this is a good approach? Another approach might be to remove the pageTitle.text() entirely since by default page_chooser.html shows get_admin_display_title. But I think adding a new data attribute is a better way.

I think I will need to add some tests also to ensure this behaviour works. I will add the tests once you confirm that this approach looks good.

• Do the tests still pass? (https://docs.wagtail.io/en/latest/contributing/developing.html#testing)
• Does the code comply with the style guide? (Run make lint from the Wagtail root)
• For Python changes: Have you added tests to cover the new/fixed behaviour?

• For front-end changes: Did you test on all of Wagtail’s supported browsers? Please list the exact versions you tested.
• For new features: Has the documentation been updated accordingly?

[squash-labs]

Manage this branch in Squash

Test this branch here: https://saptaksfix-pagechooser-display-n2fe9.squash.io

[gasman]

Thanks @SaptakS! Merged in 61e8173 (with a bit of additional logic + test to ensure that the display title is also used on the initial render for an already-populated field).