vcpkg packaging: fix portfile workarounds and add DLL export support for parsers

[matajoh]

During the vcpkg submission for Trieste 1.0.0, two issues required portfile-level workarounds that should be fixed in the Trieste source before the next release.

1. Debug headers installed to debug/include

Problem: When building with the parsers feature, cmake --install places headers into both the release and debug prefixes. vcpkg's post-build validation rejects duplicate headers under debug/include.

Current workaround (portfile):

file(REMOVE_RECURSE "${CURRENT_PACKAGES_DIR}/debug/include")

Proposed fix: The parser install(FILES ...) commands in parsers/json/CMakeLists.txt and parsers/yaml/CMakeLists.txt should be gated so they don't run for debug configurations, or the header install should be moved to a shared location in the top-level CMakeLists. Alternatively, the top-level install logic could use EXCLUDE_FROM_ALL for headers in debug builds. This is a standard CMake pattern — the install(FILES) calls for headers should not run during debug-only installs.

2. No DLL export annotations on parser libraries

Problem: The json and yaml parser libraries do not use __declspec(dllexport) / __declspec(dllimport) on their public API. On Windows, when BUILD_SHARED_LIBS is ON (the vcpkg x64-windows default), MSVC does not generate an import library (.lib), so yaml.dll fails to link against json.lib:

LINK : fatal error LNK1104: cannot open file 'parsers\json\json.lib'

Current workaround (portfile):

if(VCPKG_TARGET_IS_WINDOWS)
    set(VCPKG_LIBRARY_LINKAGE static)
endif()

This forces static linkage on Windows when the parsers feature is enabled, which works but prevents consumers from using shared libraries.

Proposed fix: Use CMake's GenerateExportHeader module to create export macros for both libraries:

include(GenerateExportHeader)
generate_export_header(json EXPORT_FILE_NAME json_export.h)
generate_export_header(yaml EXPORT_FILE_NAME yaml_export.h)

Then annotate the public API functions in json.h and yaml.h with the generated macros (e.g. JSON_EXPORT, YAML_EXPORT). The functions that need annotation are:

json.h: reader(), writer(), to_string(), equal(), unescape(), escape_unicode(), escape(), object(), array(), member(), parse_file(), apply_patch().

yaml.h: the corresponding public API functions.

This would allow the portfile to remove the VCPKG_LIBRARY_LINKAGE static workaround on Windows.

3. Minor: YAML_USE_CXX17 vs TRIESTE_USE_CXX17

In parsers/yaml/CMakeLists.txt, line 36 checks YAML_USE_CXX17 instead of TRIESTE_USE_CXX17. This is likely a typo — it means the YAML library always builds as C++20 regardless of the TRIESTE_USE_CXX17 option.

Summary

Issue	Workaround location	Fix location
Debug headers	portfile	parsers/*/CMakeLists.txt
No DLL exports	portfile (force static)	parsers/include/trieste/json.h, yaml.h, parsers/*/CMakeLists.txt
YAML_USE_CXX17 typo	none	parsers/yaml/CMakeLists.txt