Use OutputFilesProvider on aconfig_declarations_group

In the context of incremental soong, the output files
inter-module-communication will be through OutputFilesProvider.
The OutputFileProducer interface will be deprecated.

This CL also removes the unused field "intermediatePath" from
build_flag_declarations and aconfig_declarations

Test: CI
Bug: 339477385
Change-Id: I8417db7ca6ece50b3ecd807fc3b6356aa52b18e0