[topology] track connection time of neighbors (#9007)

This commit introduces a mechanism to track the connection time of
neighbors as the number of seconds since the last successful link
establishment with the neighbor. This feature requires  the
configuration `OPENTHREAD_CONFIG_UPTIME_ENABLE` to be enabled which
is now enabled by default on FTD builds. The connection time of each
neighbor is available in the `otNeighborInfo` and `otChildInfo`
structures as the `mConnectionTime` member variable. A new CLI
command, `neighbor conntime`, has been added to display the
connection time and age of all neighbors.

tests/unit/CMakeLists.txt

@@ -1052,10 +1052,17 @@ add_executable(ot-test-timer
 add_executable(ot-test-toolchain
     test_toolchain.cpp test_toolchain_c.c
 )
+
 target_include_directories(ot-test-toolchain
     PRIVATE
         ${COMMON_INCLUDES}
 )
+
+target_link_libraries(ot-test-toolchain
+    PRIVATE
+        ${COMMON_LIBS}
+)
+
 add_test(NAME ot-test-toolchain COMMAND ot-test-toolchain)
 
 target_include_directories(ot-test-timer