Bluetooth: Controller: Switch Extended Scanning to default to BT_CTLR_SCAN_AUX_USE_CHAINS

[cvinayak]

Is your enhancement proposal related to a problem? Please describe.
BT_CTLR_SCAN_AUX_USE_CHAINS is alternative new design with less RAM usage for supporting Extended Scanning of simultaneous interleaved Extended Advertising chains.
Refer to: #80056

Describe the solution you'd like
Switch Extended Scanning to default to BT_CTLR_SCAN_AUX_USE_CHAINS design in the Controller.
Deprecate use of BT_CTLR_SCAN_AUX_SET in Zephyr 4.1.99 (full v4.1.99 and v4.2.99 lifecycle having the __deprecated or __DEPRECATED_MACRO or DEPRECATED word), and remove the implementation in the v4.3.0 release.

Describe alternatives you've considered
NA

Additional context
https://docs.zephyrproject.org/latest/develop/api/api_lifecycle.html#deprecated
https://github.com/zephyrproject-rtos/zephyr/pull/84908/files#r1941874778