Add eProsima Fast DDS implementation

[zesk1999]

This PR adds the eProsima Fast DDS implementation of the DDS-XTypes interoperability test suite, following the same structure as the existing RTI and CoreDX variants.

New files:
src/cxx/variant_eprosima_fastdds.h — Fast DDS vendor implementation. Loads types from IDL files at runtime using Fast DDS Dynamic Types API, reads sample data from JSON files, and handles type registration and data comparison. Includes a workaround for a Fast DDS behavior where type incompatibility between publisher and subscriber is sometimes not reported through any callback — in that case the test would silently time out. The workaround detects when a remote endpoint is discovered but no match occurs, and reports it as an inconsistent topic.

types/idl/try_construct.idl and types/idl/unions_bitmask.idl and types/idl/unions_key_discriminator.idl — These IDL files were missing from the repository. The corresponding XML type definitions existed under types/xml/ but the IDL equivalents were never created. Without them, the relevant tests fail immediately at type loading with no topic created.

data/json/union_bitmask.json — Missing data file for bitmask union tests

Modified files
types/idl/sequences.idl — Added typedef string<10> str10 and typedef string<20> str20 at the top of the module. The Fast DDS IDL parser cannot handle sequence<string<10>, 10> syntax directly (it gives "Empty operands stack while parsing string size"). Using a typedef is valid standard IDL and is parsed identically by all other vendors.

src/cxx/test_main.cxx — Added #elif defined(EPROSIMA_FAST_DDS) vendor block and Fast DDS-specific DomainParticipantListener callbacks. All additions are inside #if defined(EPROSIMA_FAST_DDS) guards and have no effect on RTI or CoreDX builds.

[richiware]

Remove this adhoc directory. Uses a environment variable named FASTDDSHOME.

The user has to install fastdds and dependencies in this directory, for example with command colcon build --merge-install --install-dir {directory}