[26.1] Fix display bugs/usability of reports/pages

[ahmedhamidawan]

Items addressed here:

• Some directives could have either history_dataset_id OR history_dataset_collection_id and we would error out when a directive for dataset display is used but collection ID is provided. This adds a reusable DatasetOrCollectionElement that accounts for that.
• The item_url with slug like /u/{user_id}/d/{dataset_id}?preview=False never renders anything. This replaces a link to that with /datasets/${dataset_id}/display, which at least renders the entire dataset.
• Space out the editor with the CellEditor in particular spanning more of the center panel width
• Brings the add cell button inside of the previous cell to reduce whitespace
• For directives that are collapsible, change the collapse to a nicely styled existing Heading component rather than a simple anchor

Overall Changes:

Before	After

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these and all my past contributions to the core galaxy codebase under the MIT license.

[ahmedhamidawan]

FAILED lib/galaxy_test/selenium/test_pages.py::TestPages::test_standalone_page_revision_diff - AssertionError

is passing locally and seems unrelated to the changes made here.

[guerler]

1. Can you add vertical spacing to the icons inside these buttons:

2. Also it seems that the containers are too wide which is why they are clipped:

3. Suggesting to call it Insert Cell Below instead of Insert After for consistency with Insert Cell Above at the top.

4. Looks like padding is missing at the end of the button label?