[roll] Roll fuchsia [ffx][emu][pbm] Reland: Add multiple virtual device specs

Justification for reland: we will ensure that lsc
presubmits pass before landing this

This CL is addressing the issue of needing to have a more
resource constrained virtual device specification for running the
emulator on lower end machines and VMs.

There is room for improvement on the structure, naming and flexibility,
but this CL does the following:

1. Demonstrate how to add an additional virtual device spec to the PBM.
   This unfortunately is still the same for all products, but should be
   an improvement over the single definition.
2. Updates `ffx emu` with a `--device` option to select the virtual
   device spec to use. A value of `list` will list the available names.
   If not specified, it uses the first device in the list.

Usage:
`--device list` will list the available devices:

```
$ ffx emu start
file:///usr/local/google/home/wilkinsonclay/tq/fuchsia/out/default/gen/build/images/*.json#workstation.qemu-x64 \
--device list
Valid virtual device specifications are: ["qemu-x64-emu-min",
"qemu-x64-emu-recommended"]
```

Then run the emulator:

ffx emu start workstation.qemu-x64 --device qemu-x64-emu-min --headless
--engine qemu

Original-Bug: 101702
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/723123
Original-Revision: e211f9db4557581e7dd7ae7f42ca2db8abd025a6
GitOrigin-RevId: 40a4d77fb2e5fceb46e06971702561432ba548d4
Change-Id: I3d4a6c0f6164f69c05d33c9d194275954ddd9e58