target_link_libraries: Fix out-of-dir linking of a list of targets

In a case like

    target_link_libraries(targetInOtherDir PUBLIC "$<1:a;b>")

then all entries in the list need to be looked up in the caller's
scope.  Previously our `::@(directory-id)` suffix would apply only
to the last entry.  Instead surround the entire entry by a pair
`::@(directory-id);...;::@` so that the `::@` syntax can encode
a directory lookup scope change evaluated as the list is processed.

Fixes: #20204