drivers: ieee802154: improve ACK header IE config

Improves standard conformance of the IEEE802154_CONFIG_ENH_ACK_HEADER_IE
option and introduces certain "soft MAC" capabilities around header IEs:
 * Introduces types and helpers that allow driver maintainers to
   represent, parse, write and validate header IEs.
 * Introduces helper functions to access non-aligned fields in header
   IEs, namely element IDs.

Updates the only existing L2 and driver pair that uses
IEEE802154_CONFIG_ENH_ACK_HEADER_IE: OpenThread platform radio and nRF5
and improves header IE validation in the nRF5 driver.

This change should help further driver maintainers to support
OpenThread's CSL and vendor IE extensions. It is based on the rules
specified in RFC #61227.

It is also a precondition to generically support both, "soft MAC" and
"hard MAC", approaches to header IEs in the TSCH protocol, namely the
time synchronization IE.

Fixes: #62940

Signed-off-by: Florian Grandel <fgrandel@code-for-humans.de>