[jansson] update to 2.15.1

[ricardoofnl]

• Changes comply with the maintainer guide.
• SHA512s are updated for each updated download.
• The "supports" clause reflects platforms that may be fixed by this new version, or no changes were necessary.
• Any fixed CI baseline and CI feature baseline entries are removed from that file, or no entries needed to be changed.
• All patch files in the port are applied and succeed.
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• Exactly one version is added in each modified versions file.

https://github.com/akheron/jansson/releases/tag/v2.15.1

[BillyONeal]

GPT 5.5 observes the following and wrote ricardoofnl#2 which fixes it for you.

• The installed Windows Debug pkg-config metadata appears to advertise Libs: -ljansson, while the Debug library is installed as jansson_d.lib, causing pkg-config Debug consumers to fail linking with LNK1104. This appears pre-existing because the portfile and upstream jansson.pc.in are unchanged except for the version.
• The port declares "license": "MIT", but upstream's license text notes exceptions, including non-MIT src/dtoa.c; upstream's default CMake option includes that code via USE_DTOA=ON. This also appears pre-existing.

[ricardoofnl]

Both observations are correct and are now fixed, with one correction to the license identifier.

• Debug pkgconfig: confirmed. Upstream sets CMAKE_DEBUG_POSTFIX=_d on Windows (jansson_d.lib) but jansson.pc keeps -ljansson. The portfile now rewrites -ljansson -> -ljansson_d in the debug .pc on Windows (non-release-only builds).
• License: confirmed that USE_DTOA defaults ON, so src/dtoa.c is compiled in, and its terms are not MIT. But the exception is not HPND: SPDX has a dedicated identifier dtoa (David M. Gay dtoa License) whose text matches jansson's src/dtoa.c exception verbatim, whereas HPND has a different "name not used in advertising" clause the dtoa license lacks. So I used MIT AND dtoa rather than MIT AND HPND. Also switched the copyright install to vcpkg_install_copyright as in your PR.

vcpkg accepts MIT AND dtoa and the port builds. Thanks for the catch on both.