Fix dependencies on targets linked through object libraries

When an object library is used via `target_link_libraries`, any targets
listed in the object library's `INTERFACE_LINK_LIBRARIES` closure should
become direct dependencies of the consuming target.  However, these were
accidentally left out by `cmComputeTargetDepends::CollectTargetDepends`
because object libraries are encountered through external object sources
first and then added to the `emitted` set which blocks them from being
processed as link dependencies.

This was not noticed by the test case in commit bab24e782c
(target_link_libraries: Propagate dependencies of object libraries,
2018-12-10, v3.14.0-rc1~260^2) because the relevant dependency appears
transitively through the object library target itself.

Re-order the logic to process link dependencies first, and then external
object sources.  That way object libraries used via
`target_link_libraries` will be treated as such by dependency analysis.

This also adds missing backtrace information for object libraries used
via `target_link_libraries`.  The missing information was mentioned in a
FIXME comment in the RunCMake.FileAPI test added by commit ea0a060168
(fileapi: Add test for codemodel v2, 2018-11-09, v3.14.0-rc1~257^2~7).
That comment itself was dropped by commit a0de350e2f (FileAPI test:
Break gen_check_targets() into JSON files, 2020-02-07), but we can now
update the corresponding location in the `.json` files to have the
now-expected backtrace information.

Fixes: #20421

Tests/ObjectLibrary/Transitive/CMakeLists.txt

@@ -5,3 +5,8 @@ add_library(FooObject1 OBJECT FooObject.c)
 target_link_libraries(FooObject1 PRIVATE FooStatic)
 add_executable(Transitive1 Transitive.c)
 target_link_libraries(Transitive1 PRIVATE FooObject1)
+
+add_library(FooObject2 OBJECT FooObject.c)
+target_link_libraries(FooObject2 INTERFACE FooStatic)
+add_executable(Transitive2 Transitive.c)
+target_link_libraries(Transitive2 PRIVATE FooObject2)