Added ability to see changelog from the add-on store and Updatable add-ons dialog (#18816)
Fixes #14041
Summary of the issue:
Users may want to see changes included in the current version of add-ons, especially to decide if they want to update them, and to get an idea of new features, bug fixes and so on.
Description of user facing changes:
In the add-on store, a new action allows to see changes for the current version of add-ons which specify this information.
In the Updatable add-ons dialog, the virtual list used in other tabs of the store is presented, instead of the old small list, so that the changelog, if available, can be opened from the context menu to decide if add-ons should be updated to the available version.
List of changes will be shown in browse mode. If changes are writen in markdown, they will be rendered in formatted HTML. The title of that message will show the add-on version name, and buttons will be available to copy the info and close the browseable message.
Description of developer facing changes:
Add-on models have a new changelog property.
The self.addonsList of the UpdatableAddonsDialog class is a subclass of the AddonVirtualList.
Description of development approach:
Created a new action to show the changelog, when available, similar to other actions.
Added changelog to add-on models.
In the Updatable add-ons dialog, the same list used in the store dialog is presented, so that changelog can be opened from the context menu.