Introduce aconfig_declarations property in udc-mainline-prod

Currently, Soong changes in aosp are not merged to udc-mainline-prod,
while the mainline projects changes from aosp are merged. This leads to
a conflicting build configuration issue for aosp-first projects, which
want to maintain consistent bp module definition between aosp and main.

In order to support specifying `aconfig_declaration` property in aosp
for mainline projects, this change adds the property to the module
definition while not performing any build actions, in order to resolve
presubmit failures in udc-mainline-prod when specifying the property in
aosp changes.

Cherry-picking the aosp changes that introduces the property is not an
option, as the flagging infra is not expected to be imported to
udc-mainline-prod.

Test: m nothing --no-skip-soong-tests
Bug: 315027929
Merged-In: I37becd1b9dd9069d7ac4abed130906df30b3fdf4
Change-Id: Ie467c1dd4a36774f6268452fae8c054b9b3ad7d9