Split Windows library build scripts from CI

[HertzDevil]

This PR extracts the build scripts for the various third-party libraries in the Windows CI jobs into individual PowerShell scripts.

These scripts can be run from any directory. They all require CMake and Git; setup.ps1 will try to detect them from several common locations, even if they aren't present in %PATH%. Additionally, building PCRE requires 7-Zip, and building OpenSSL requires NASM and Strawberry Perl.

All those scripts support static and dynamic builds; the latter adds -dynamic to the names of all import libraries, in accordance with #13473. To build the libraries as DLLs, start from the MSVC developer prompt: (Strawberry Perl adds a lot of things to %PATH%, so it is a good idea to use the portable installation and keep %PATH% intact outside building OpenSSL)

> powershell
PS> .\etc\win-ci\build-gc.ps1 -BuildTree deps\gc -Version 8.2.2 -AtomicOpsVersion 7.8.0 -Dynamic
PS> .\etc\win-ci\build-pcre.ps1 -BuildTree deps\pcre -Version 8.45 -Dynamic
PS> .\etc\win-ci\build-pcre2.ps1 -BuildTree deps\pcre2 -Version 10.42 -Dynamic
PS> .\etc\win-ci\build-iconv.ps1 -BuildTree deps\iconv -Dynamic
PS> .\etc\win-ci\build-ffi.ps1 -BuildTree deps\ffi -Version 3.3 -Dynamic
PS> .\etc\win-ci\build-z.ps1 -BuildTree deps\z -Version 1.2.13 -Dynamic
PS> .\etc\win-ci\build-mpir.ps1 -BuildTree deps\mpir -Dynamic
PS> .\etc\win-ci\build-yaml.ps1 -BuildTree deps\yaml -Version 0.2.5 -Dynamic
PS> .\etc\win-ci\build-xml2.ps1 -BuildTree deps\xml2 -Version 2.11.3 -Dynamic
PS> exit
> ...\strawberry-perl\portableshell.bat /SETENV
> powershell
PS> .\etc\win-ci\build-openssl.ps1 -BuildTree deps\openssl -Version 3.1.0 -Dynamic

This will place all the import libraries inside .\libs and all the DLLs inside .\dlls. To build static libraries simply remove the -Dynamic; static and dynamic builds should use separate build trees to avoid surprising behavior.

This PR also upgrades libxml2 from 2.10.3 to 2.11.3, and OpenSSL from 3.0.7 to 3.1.0.

Eventually the scripts will be moved to a completely different place where all the libraries (and possibly the installer too) will be published as a single artifact.