osgEarthCesium ported to Cesium Native 0.52.1.

[remoe]

The following changes to Cesium Native are relevant for this port:

• Renamed ImageCesium to ImageAsset (v0.41.0)
• Switched from gsl::span to std::span throughout the library and API. The GSL library has been removed. (0.42.0)
• Refactored CreditSystem (v0.47.0)

I've not tested FindCesiumNative.cmake because I use my own. I built Cesium Native with own CMake based package system but I let build the static library dependencies with vcpkg. But the current one should partially work as well.

Here is a part of my draft version:

...

# 1) Blend2D (used by CesiumVectorData)
find_package(blend2d REQUIRED
  PATHS ${CESIUM_NATIVE_DEP_PREFIX}
  NO_DEFAULT_PATH
)

# 2) picosha2 (header-only; some builds have no *Config.cmake)

find_package(picosha2 CONFIG QUIET
  PATHS ${CESIUM_NATIVE_DEP_PREFIX}
 NO_DEFAULT_PATH
)

# picosha2 doesn't provide a config in vcpkg 
if(NOT picosha2_FOUND)
  find_path(PICOSHA2_INCLUDE_DIR
    NAMES picosha2.h picosha2/picosha2.h
    PATHS ${CESIUM_NATIVE_DEP_PREFIX}
    PATH_SUFFIXES include Include
    NO_DEFAULT_PATH
  )

  add_library(picosha2::picosha2 INTERFACE IMPORTED)
  set_target_properties(picosha2::picosha2 PROPERTIES
    INTERFACE_INCLUDE_DIRECTORIES "${PICOSHA2_INCLUDE_DIR}"
  )
endif()

find_package(cesium-native REQUIRED)

set(CESIUM_NATIVE_IMPORT_LIBRARIES "")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "${CESIUM_NATIVE_DIR}")

list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "Cesium3DTilesSelection")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "CesiumIonClient")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "CesiumRasterOverlays")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "Cesium3DTilesContent")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "Cesium3DTilesReader")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "Cesium3DTiles")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "CesiumQuantizedMeshTerrain")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "CesiumGltfContent")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "CesiumGltfReader")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "CesiumGltf")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "CesiumGeospatial")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "CesiumGeometry")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "CesiumAsync")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "CesiumJsonReader")
list(APPEND CESIUM_NATIVE_IMPORT_LIBRARIES "CesiumUtility") 

if(cesium-native_FOUND)
    set(CESIUM_NATIVE_FOUND TRUE)
    add_library(OE::CESIUM_NATIVE INTERFACE IMPORTED)
    set_property(TARGET OE::CESIUM_NATIVE PROPERTY
        INTERFACE_LINK_LIBRARIES ${CESIUM_NATIVE_IMPORT_LIBRARIES} )
endif()

include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(CesiumNative DEFAULT_MSG CESIUM_NATIVE_FOUND)

...