Show downloading add-ons in updatable add-ons tab (#16044)
Fixes #16015
Summary of the issue:
Issue 1: When downloading an update from the updatable add-ons tab, the add-on disappears from the list.
Issue 2: if an add-on has been installed from an external source, the NVDA GUI allows you to attempt to update the add-on.
NVDA should not allow users to install or update an add-on with the same ID if the add-on is already pending installation.
Issue 3
Installing incompatible add-ons would redraw the whole listing rather than just refreshing the status.
Description of user facing changes
Add-ons will no longer disappear from the updatable add-ons tab when updating them.
External add-ons pending install will correctly show up as installed pending restart in the add-on store list.
Ensured installing incompatible add-ons did not redraw the list.
Description of development approach
Add downloading/installing statuses to the updatable add-ons tab.
Ensured externally installed add-ons would return the correct status from getStatus
Checked for usages of refresh after getAddon.
