Use `Packed*Array` over `Vector<T>` in Variant #21772

Job	Run time
📊 Static checks / Code style, file formatting, and docs	36s
🍏 iOS / Template (target=template_release)	14m 16s
🤖 Android / Template (target=template_release)	28m 55s
🐧 Linux / Editor w/ Mono (target=editor)	35m 24s
🐧 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)	36m 21s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	29m 58s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	27m 29s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	21m 33s
🍎 macOS / Editor (target=editor, tests=yes)	25m 8s
🐧 Linux / Template w/ Mono (target=template_release)	18m 6s
🌐 Web / Template w/o threads (target=template_release, threads=no)	21m 16s
🍎 macOS / Template (target=template_release)	22m 43s
🐧 Linux / Minimal template (target=template_release, everything disabled)	13m 49s
🏁 Windows / Editor (target=editor, tests=yes)	41m 46s
🏁 Windows / Template (target=template_release)	31m 35s
🪲 Godot CPP / Build and test Godot CPP	6m 54s
	6h 15m 49s

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