[PLAN] Users should be able to configure their own shortcut sets

Problem/Motivation

Shortcut module is flagged as an unmaintained module or a module that is not highly popular in Drupal installs, according to #3311180: [meta] Determine how to make Shortcut module more useful and maintainable there's a suggestion to deprecate it and move it to contrib. However the navigation and dashboard initiatives consider it useful as per comments in #3311180-13: [meta] Determine how to make Shortcut module more useful and maintainable that reference #3373292: [Plan] Administration main navigation modernization and #3244581: Enhance user experience with customizable dashboards.
Currently the implementation of the shortcut module include bundles in the form of shortcut sets but it is a site-wide implementation and they're not customisable by user or any other criteria but the set itself, this lack of flexibility supposes a limitation and it might be the main reason for it to be a not-so-popular Drupal core module.

Proposed resolution

Based on the results of the survey, this project aims to provide an approach to enable users to be able to customise their own shortcut sets, and an additional plugin should support per-role shortcut sets. Further plugins can be provided in contrib, for example a per group shortcut set or one per Commerce store.

Quantitative user research will be done to gather information regarding whether such feature would be considered interesting by Drupal users in the form of a survey, and qualitative user interviews will be performed to gather feedback once the feature reaches Beta status.

User research

• User survey: #3432935: User Research: Survey regarding bookmarking features on Drupal
• User interviews #3452488: User Research: Interviews to evaluate improvements on the shortcut module

Beta Criteria

• #3432939: Shortcut set default plugin
• #3432940: Users should be able to customise their own shortcuts
• #3432941: Users with enough privileges should be able to customise shortcut sets per role

The final part of this project, after the scope for beta is accomplished, will include opening an IDEA issue + an MR against Drupal core for consideration.