Use libxml2 for DDoc parsing #1223

Job	Run time
Run Coverity tests	0s
Run CodeQL tests	4m 51s
Build on macOS for osx	2m 32s
Build on Fedora 39	1m 55s
Build on macOS for ios	1m 28s
Build on Fedora 40	1m 22s
Deploy pages	0s
Build on macOS for iossimulator	1m 41s
Build on Ubuntu 20.04	3m 16s
Build on macOS for androidarm	1m 32s
Build on Ubuntu 22.04	3m 59s
Build on macOS for androidarm64	1m 43s
Build on Ubuntu 23.10	3m 24s
Build on Windows (143, x86)	8m 59s
Build on macOS for androidx86_64	1m 30s
Build on Ubuntu 24.04	4m 3s
Build on Windows (143, x64)	9m 59s
Build on Windows (142, x86)	8m 24s
Build on Windows (142, x64)	8m 36s
	1h 9m 14s

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