Add an icon picker for adb devices and speaker and VR headset icons

[PyFlat-JR]

What does this PR do?

Lets adb devices pick their icon and adds speaker and VR headset icons.

• adb devices get the same Icon field Bluetooth devices had (default phone), so a tablet or a Quest no longer shows as a phone.
• New icons: Speaker and VR headset, for both adb and Bluetooth. In the "by device type" scheme the speaker is teal and the VR headset uses the headset's pink.
• adb and Bluetooth store the choice under one kind key. Existing Bluetooth entries keep working, since the reader falls back to bluetoothKind.
• The icon options are localized strings instead of raw values like mouse, and the field is labelled "Icon" instead of "Kind".
• The "Quest 2" sample in the previews uses the VR headset icon.

Checklist

• I have read AGENTS.md and CONTRIBUTING.md.
• dotnet build and dotnet test pass locally (0 warnings, 278 tests).
• I updated README.md / AGENTS.md if this changes what they describe.
• If this touches a device backend: I tested it against the real hardware (see below).

Device/hardware tested against (if applicable)

Not a device backend.