update-reset: add new command.

[MikeMcQuaid]

Add new brew update-reset command to provide a helpful troubleshooting fallback to fetch and reset all repositories. This could have lived in
brew update but it makes sense to avoid the complexity of sharing logic between these scripts and keeping this one simpler.

[MikeMcQuaid]

@ilovezfs Any thoughts on this (the general approach; ignore failing CI)?

[ilovezfs]

How is the use case here different from update -f? If an additional level of force is needed, why not make that another option to update rather than creating a whole new command?

Also, I think we can pretty much bet the house that this will cause people to lose work. Not sure how to dangle a neon sign around it indicating as such.

[MikeMcQuaid]

How is the use case here different from update -f? If an additional level of force is needed, why not make that another option to update rather than creating a whole new command?

This will blindly reset everything and not put people back to their branch or keep their work. It's the update-reset-i-dont-know-git command, basically, that we often tell people to run manually. We can guard it against the HOMEBREW_DEVELOPER or homebrew.devcmdrun. It's not documented anywhere so I think people are unlikely to just randomly run it to see what happens.

Creating a new command is to avoid adding additional complexity to update.sh and to keep this super reliable and simple. It intentionally bypasses a bunch of our e.g. shim code etc. which could stop people being able to update.

[MikeMcQuaid]

@ilovezfs Thoughts? I don't mind renaming this accordingly or making the checks suggested.

[ilovezfs]

Nope, sounds fine to me. It will be good to have this. If we later decide to roll it into update as a --foo, that won't detract from the utility of having this now.