[roll] Roll fuchsia [ffx] Show context for FfxContext wrappers.

This change updates `user_message` and `bug_context` to properly attach
context without duplicating messages, and allowing for users of `ffx` to
see error contexts more clearly.

Before this change, if a user were to have a default target that was set
incorrectly (e.g. there is no target named "foobar"):

Before this change we'd see this kind of error:

```
$ ffx target reboot -b
Failed to create target proxy
```

This doesn't tell us much of anything.

After this change we see:

```
$ ffx target reboot -b
Failed to create target proxy: Timeout attempting to reach target "foobar"
```

Which would at least tell us we're attempting to locate a target named
"foobar"

Some changes had to be made to existing code that wraps errors in order
to prevent duplication, namely that one needs to unwrap the source
`anyhow::Error` and rewrap it to prevent duplicating the error
messaging/chain.

Original-Fixed: 410051423

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1254328
Original-Revision: 6874883f5b2252bb5a6d259c3a0f5c6fbdcf901a
GitOrigin-RevId: d5b8aa63d604cff7e46a207fb6c53326c087b22a
Change-Id: I537a693e7715e8473cc597862acc5a7210cc45c2