Add changes to enable searching for .msg files in sub-directories

[aditya2592]

Fix for #1188

[aditya2592]

Failure in this test seems unrelated to the change in this PR

[james-rms]

Are you able to add a test for this new behavior?

[james-rms]

Please include some equivalent of this patch to prevent the message definition cache mistaking CompressedImage.msg for Image.msg. Also, please add a test to this repo to ensure that this behavior is correct going forward.

[aditya2592]

Please include some equivalent of this patch to prevent the message definition cache mistaking CompressedImage.msg for Image.msg. Also, please add a test to this repo to ensure that this behavior is correct going forward.

Patch has been added. Is there any relevant documentation to compile and run tests in this repo? Or should I follow the normal colcon test process? Also is there a suggested test file to add it to?

[james-rms]

test_message_definition_cache.cpp contains tests for this component, and includes several instances of searching for message definitions within the rosbag2_storage_mcap_testdata package. I'd recommend adding a nested subdirectory definition to the testdata package and testing that it can be found.