[ls-qpack] Update, revise

[dg0yt]

Patch upstreaming at https://github.com/litespeedtech/ls-qpack/pulls.

[dg0yt]

This doesn't "DEPEND" on upstream changes. Of course we could wait for upstream acceptance of the changes, but in the meantime the port is partially broken.

[Mengna-Li]

Let's wait for upstream approve or response.

[dg0yt]

This blocks improvements to downstream ports.

[dg0yt]

In particular, this PR enables the removal of pkg-config from the transitive usage requirements for the cmake config. Which is one step towards fixing the sad state of msh3's exported usage.

[talregev]

@Mengna-Li I agree with @dg0yt. He already notified upstream.
I already have similar condition when I export namespace cmake in ls-qpack. It was first merge in vcpkg, then upstream merge my PR without any response.
litespeedtech/ls-qpack#59
#40652

If you still don't agree, please review this port and we can have vcpkg team review, and let all team decide.

Thank you for your help and time to review this port 🙏🏻