wifi: Helper functions for invoking hidl cont callbacks

The helper functions are used to invoke an internal method which
implements the functionality and then invoke the HIDL callback
with the return values.

HIDL's auto-generated code uses on-stack callbacks to return
non-primitive/multiple values from HIDL methods. This is unwieldy and
the implementation of the method's functionality gets mixed up with the
semantics of handling these callbacks. This tries to hide the semantics
of HIDL auto-generated code from the functionality.

Converted all IWifi methods to use these new helper functions.

Bug: 32337072
Test: Compiles
Change-Id: I57cbafcc2ecb52ec5055f4bd80bc064bd438b850