Add bounded string support in C++

[aprotyas]

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This PR consists of two parts:

• [rosidl_runtime_cpp] Introduces a bounded_basic_string class.
• [rosidl_generator_cpp] Correctly map bounded string/wstring IDL types to bounded_basic_string types, rather than std::basic_string types.

Fixes https://github.com/ros2/rosidl/issues/637.

Signed-off-by: Abrar Rahman Protyasha [email protected]

[fujitatomoya]

@aprotyas any progress or plan on this?

[aprotyas]

@fujitatomoya it'll be a while before I can get back to this (school gets in the way!), but I have a WIP BoundedString implementation that I'd integrate into this PR.

Feel free to take over this PR though. Let me know if you do.