[iguana] Update to 1.2.0

[xiaozhuai]

Update to 1.2.0

[BillyONeal]

GPT 5.5 suggests that this may be broken:

• The installed headers are not self-contained. Upstream 1.2.0 includes frozen/string.h and frozen/unordered_map.h from iguana/field_reflection.hpp and iguana/ylt/reflection/template_string.hpp, but the port only installs iguana/ headers and declares only protobuf as a dependency. See portfile.cmake and vcpkg.json. A direct consumer can fail with fatal error C1083: Cannot open include file: 'frozen/string.h'.

Fix: prefer adding a manifest dependency on the existing frozen port if it provides the required include layout. Otherwise, install upstream's frozen/ headers and ensure the package copyright covers that vendored Apache-2.0 code. See the manifest dependency documentation and maintainer guide.

Non-blocking issues

• Upstream iguana/version.hpp still reports IGUANA_VERSION 100005 // 1.0.5. This appears pre-existing and upstream-owned, but may confuse consumers relying on the macro.

[xiaozhuai]

@BillyONeal All of the issues mentioned above have been resolved. Please review this pr again.