[META] Improve Entity selection (single / multiple) UX

Problem/Motivation

Selecting entities in Entity Browser using an Entity Browser View display currently has several flaws that make using Entity Browser hard for regular users.
This spreads across various issues, so this is a META issue trying to wrap things up and improve the overall UX on this.

See the related and child issues.

Clearly related:

✨ Open entity browser with one click from Entity Browser IEF widget Needs review
#2853751: Selecting "Automatically submit selection" in widget plugin view leads to error →
🐛 Missing tableselect dependency in view Needs work
🐛 Issue with selections + single cardinality Active
✨ Bulk select form does not submit all selected items from different pages through pager Active
💬 Hide already selected items? Active
🐛 Automatically submit selection skips field validation in View widget Needs work
🐛 "Select this item" isn't a good field label for screenreaders Active
🐛 Wrong behavior of item selection in Firefox browser Active
#3314103: Add completion message and redirect url to the standalone display →
#2922337: Alter the "Select entities" button text →
📌 Make submit button on modal always visible Needs review
#2825555: Improve Field Widget UX for single-cardinality File/Image fields →
✨ Position the main form actions to the bottom of IFrame Needs work
#2644018: Merge Edit and Delete buttons in Entity Reference widget into an operations field →
#2977251: Wrap current selection action buttons into a actions form item →
#2959832: Double click on a row should add to selection and submit →

Slightly related:

#2755261: Add a splash TAB to entity browser to increase usability →
💬 How to create a "select all" checkbox with views bulk select form Needs review
✨ Entity Browser Entity Reference Widget: wrap getCardinality() in own function Needs review
🐛 Error messages are not being displayed correctly in modal windows Needs work
✨ Preserve the previous selection when using replace and closing the modal Needs work
🐛 Multi select over different pages resets filter Active
💬 Used entity browser selection display does not support preselection Active
✨ Provide hook to alter view executable before render in view widget Needs work
🐛 The "id" attribute disappears from the checkbox Needs work
🐛 Validate widget entity type and bundles Needs review
✨ Configurable checkbox label RTBC
🐛 Cannot add a label to the the checkbox column (Entity browser bulk select form) Needs review
🐛 Allow scrolling of main page RTBC
#3247047: No selection display still showing selection →
🐛 Improve default widget labels Needs work

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes