Ability to download and install updates from other channels

[jmdaweb]

Is your feature request related to a problem? Please describe.

Currently, installed or portable copies of NVDA can only be updated to the next release for their respective channel. For example, stable releases can be updated only to the next stable, alpha to another alpha, and so on. Beta releases are an exceptional case: they go through rc to stable, so when a new beta is available, users must install it manually.

Describe the solution you'd like

Features from update channel selector add-on may be integrated into core. Currently, this add-on provides asettings panel in NVDA settings dialog which allows you to change the update channel. Once changed, when the user goes to NVDA help menu and checks for updates, the current version for that channel is downloaded and installed. This is useful, for example, to install an alpha snapshot, test a new feature and return quickly to stable, without additional portable copies nor browsing the web to download additional files. As suggested in the nvda-addons mailing list, these settings could be added to the advanced settings panel.

Describe alternatives you've considered

Additional context