Push Hidden_api inside HiddenAPIFlagFileProperties

All usages of HiddenAPIFlagFileProperties use it as the type of a
Hidden_api field. This change pushes the field inside the struct and
just embeds the struct inside the structs that need it making it
simpler and more consistent with how the HiddenApiPackageProperties
struct is used.

This is extracted as a separate change as while the change is simple
it does affect a lot of lines. Keeping it separate makes it easier to
review the changes.

Bug: 240406019
Test: packages/modules/common/build/mainline_modules_sdks.sh
      # Ran the previous command with and without this change to make
      # sure that this change does not change the sdk snapshot
      # contents.
Change-Id: I664453029574ef68dc5712f7bf137a1a6e78e864