Bluetooth: Host: Add support for Advertising Coding Selection

Adds API for Advertising Coding Selection.

Introduces two new advertising options to configure the advertiser's
requirement concerning coding scheme when LE Coded PHY is configured.
While the Bluetooth v6.0 specification makes a distinction betweeen
preferred and required advertising PHY options, a simplification is
made to only expose the required PHY options. Inline with how LE Coded
PHY is implemented; this API will set both the primary and secondary
advertising PHY's to the same coding scheme.

The support is enabled by CONFIG_BT_EXT_ADV_CODING_SELECTION, and requires
a controller that selects CONFIG_BT_CTLR_ADV_EXT_CODING_SELECTION_SUPPORT.

Signed-off-by: Thomas Deppe <thomas.deppe@nordicsemi.no>