Bluetooth: GAP name and appearance

[alwa-nordic]

There are at least 4 change requests to do with the GAP name and appearance API.

• bluetooth: settings: Make BT name persistance an option #93700
  Dynamic should not imply persistent.
• Bluetooth: Host: BT_DEVICE_NAME should be mutually exclusive with BT_DEVICE_NAME_DYNAMIC #93769
  The static value CONFIG_BT_DEVICE_NAME is a confusion hazard when BT_DEVICE_APPEARANCE_DYNAMIC=y.
• bluetooth: GAP Device Name and Apperance write callbacks #93723
  There is a lack of observer API for GAP values.
• Thread safety: Bluetooth: Host: Introduce new GAP Device Name APIs #88896
  The current API is fundamentally thread-unsafe.

I think it's best to address all these problems together. RFCs welcome.

[rkel]

Note that there is PR #93946 already for #93723.