chore(lanelet2_map_validator): automate test code compilation

[TaikiYamada4]

Description

This PR renews the compilation approach so that the contributors doesn't have to declare their test codes in the CMakeLists.txt file.

In addition, the test codes are also categorized as same as the ones in the src directory.

Related links

None

Tests performed

1. Tested that clean building works perfectly.
2. Tested that colcon test works perfectly
3. Tested that ros2 run autoware_lanelet2_map_validator autoware_lanelet2_map_validator works perfectly with sample_map.osm

Notes for reviewers

Renewed in here #183

Interface changes

None

Effects on system behavior

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