After evaluating the INTERFACE_INCLUDE_DIRECTORIES, of a target in a
generator expression, also read the INTERFACE_INCLUDE_DIRECTORIES of
its link interface dependencies.

That means that code such as this will result in the 'user' target
using /bar/include and /foo/include:

 add_library(foo ...)
 target_include_directories(foo INTERFACE /foo/include)
 add_library(bar ...)
 target_include_directories(bar INTERFACE /bar/include)
 target_link_libraries(bar LINK_PUBLIC foo)

 add_executable(user ...)
 target_include_directories(user PRIVATE
    $<TARGET_PROPERTY:bar,INTERFACE_INCLUDE_DIRECTORIES>)

Also process the interface include directories from direct link
dependencies for in-build targets.

The situation is similar for the INTERFACE_COMPILE_DEFINITIONS. The
include directories related code is currently more complex because
we also need to store a backtrace at configure-time for the purpose
of debugging includes. The compile definitions related code will use
the same pattern in the future.

This is not a change in behavior, as existing code has the same effect,
but that existing code will be removed in follow-up commits.