Add overlay for 8849 (Unihertz) Tank Mini

[PeterCxy]

I am not sure if the Unihertz Tank Mini will use the same model / fingerprint string, but what I have is the 8849-branded version, so this is what it is.

If the Unihertz one is different maybe we can change the fingerprint regex later.

[PeterCxy]

test failures:

• config_wifi_tcp_buffers, status_bar_icon_size, and status_bar_icon_size_sp all do exist
• Priority is set to 8849 because, uh, it's funny.

[phhusson]

config_wifi_tcp_buffers

Ok but why do you need to set it? I fail to see how this is hardware-specific

[phhusson]

Uh it actually doesn't exist anymore. It's a packages/modules/Wifi value now, not a frameworks-res one

[PeterCxy]

Right. config_wifi_tcp_buffers is now removed, but the other two are still needed.