Implement a base class `SkeletonModifier3D` as refactoring for nodes that may modify `Skeleton3D` #26756

Job	Run time
📊 Static checks / Code style, file formatting, and docs	3m 24s
🤖 Android / Template (target=template_release)	25m 20s
🍏 iOS / Template (target=template_release)	16m 46s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	4m 19s
🌐 Web / Template w/o threads (target=template_release, threads=no)	19m 22s
🐧 Linux / Editor w/ Mono (target=editor)	33m 27s
🐧 Linux / Editor with doubles and GCC sanitizers (target=editor, tests=yes, dev_build=yes, scu_build=yes, precision=double, use_asan=yes, use_ubsan=yes, linker=gold)	30m 3s
🍎 macOS / Editor (target=editor, tests=yes)	19m 25s
🏁 Windows / Editor (target=editor, tests=yes)	40m 17s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	31m 43s
🍎 macOS / Template (target=template_release)	16m 2s
🏁 Windows / Template (target=template_release)	32m 21s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	26m 51s
🐧 Linux / Template w/ Mono (target=template_release)	19m 55s
🐧 Linux / Minimal template (target=template_release, everything disabled)	46s
🪲 Godot CPP / Build and test Godot CPP	6m 58s
	5h 26m 59s

Provide feedback