Switch nav2_costmap_2d to modern CMake idioms.

[clalancette]

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Basic Info

Info	Please fill out this column
Ticket(s) this addresses	Follow-up to #4357
Primary OS tested on	Ubuntu 24.04
Robotic platform tested on	N/A
Does this PR contain AI generated software?	No

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Description of contribution in a few bullet points

This PR updates nav2_costmap_2d to use modern CMake idioms. In particular:

1. Switch from ament_target_dependencies to target_link_libraries everywhere, since the latter is a superset of the features.
2. Get rid of the unnecessary ALIAS library. This was only ever used for linking for tests in this package; all other one downstream libraries will get that library name from ament_export_targets()
3. Make sure to call ament_export_include_directories and ament_export_libraries to make sure any "old" CMake projects can properly use this one.
4. Make sure to properly export all of the dependencies of this package.

Description of documentation updates required from your changes

None needed.

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Future work that may be required in bullet points

This is part of a larger series updating all of the navigation2 packages to conform to modern CMake standards. There will be follow-up PRs for other packages.

For Maintainers:

• Check that any new parameters added are updated in docs.nav2.org
• Check that any significant change is added to the migration guide
• Check that any new features OR changes to existing behaviors are reflected in the tuning guide
• Check that any new functions have Doxygen added
• Check that any new features have test coverage
• Check that any new plugins is added to the plugins page
• If BT Node, Additionally: add to BT's XML index of nodes for groot, BT package's readme table, and BT library lists