[lunasvg] Add usage

[JonLiu1993]

Fixes #30186

Lunasvg does not export anything after installation, I add the usage.
Tested the usage successfully by lunasvg:x64-windows:

lunasvg provides CMake targets:

    # this is heuristically generated, and may not be correct
    find_package(unofficial-lunasvg CONFIG REQUIRED)
    target_link_libraries(main PRIVATE unofficial::lunasvg::lunasvg)

• 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
• Any fixed CI baseline entries are removed from that file.
• Any patches that are no longer applied are deleted from the port's directory.
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• Only one version is added to each modified port's versions file.

[dg0yt]

Does this config help with any usage requirements beyond what documenting find_path and find_library in usage could do?
Adding unofficial config everywhere (and not upstreaming it) effectively still creates vcpkg lock-in.

[JonLiu1993]

Does this config help with any usage requirements beyond what documenting find_path and find_library in usage could do? Adding unofficial config everywhere (and not upstreaming it) effectively still creates vcpkg lock-in.

@dg0yt, Thanks for your review, what exactly are you worthy of meeting any other requirements? I just checked locally whether the files generated under its packages\ folder are correct, and tested its exported usage locally.

[dg0yt]

I didn't claim it wouldn't be working.
This change is adding a patch, which is intrusive, to add an unofficial CMake config which doesn't exist outside the vcpgk world. I'm not convinced that this is more beneficial than useful.

With regard to transitive usage requirements, I found only the following: C++ linkage, libm for non-windows.

With regard to upstream, sammycage/lunasvg#84 may need support.

[Pospelove]

Thanks for taking a look at this port

Please consider also updating to the latest commit. The current version is outdated and lacks critical patches Like UB fix sammycage/lunasvg#123 and much more

Thanks again

[aeris170]

Sorry to rush things but, could we merge this?

[JonLiu1993]

Since the addition of upstream usage caused issue for users, the latest upstream version restored the changes about usage in CMakeLists. I updated to the latest version and added a patch to provide unofficial usage.

[dg0yt]

The upstream issues were caused by build-internal changes, not by the exported config.
I would prefer you wouldn't add an unofficial config patch at this point and submitted a PR upstream instead.
I doesn't hurt to merge one more port update without exported config.

[JonLiu1993]

I have commit a PR for Upstream sammycage/lunasvg#132

[JonLiu1993]

I submitted a PR upstream, but there has been no response for a month and a half, I think we can merge this PR first for users to use.

[JonLiu1993]

PR #32510 Deleted the historical "git-tree" when updating lunasvg, I restore it here.

[BillyONeal]

Oops 😳. Thanks!

[sakiodre]

My mistake, thanks for the fix!

[BillyONeal]

Thanks!

[aeris170]

Thanks for merging fast!