ndk_library depends on the correct arch variant of cc_library_headers

Previously before aosp/3249712, ndk_library was assumed to depend only
on ndk_headers, which do not have any variants.

As ndk_library can now depend on cc_library_headers which has many
variants for arch, sdk, and more, the previous assumption no longer
holds.

Therefore, when ndk_library makes a dependency to its
export_lib_headers, it now uses either AddFarVariationDependency with
(for ndk_headers) or AddVariationDependency (for others) depending on
which module type it depends on.

Bug: 357711733
Test: build with  https://r.android.com/q/topic:%22no-cpp-in-ndk-2%22
Change-Id: Id0957e82736bd458e15674ffc45ca32b1e3a7250