Add miscellaneous documentation to some classes #335

Job	Run time
📊 Static checks / Code style, file formatting, and docs	25s
🍏 iOS / Template (target=template_release)	20m 34s
🤖 Android / Template (target=template_release)	28m 5s
🍎 macOS / Editor (target=editor, tests=yes)	24m 49s
🐧 Linux / Editor w/ Mono (target=editor)	35m 39s
🍎 macOS / Template (target=template_release)	13m 45s
🐧 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)	38m 40s
🌐 Web / Template (target=template_release)	20m 40s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	31m 35s
🏁 Windows / Editor (target=editor, tests=yes)	41m 25s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	28m 5s
🏁 Windows / Template (target=template_release)	30m 2s
🐧 Linux / Template w/ Mono (target=template_release)	23m 21s
🐧 Linux / Minimal template (target=template_release, everything disabled)	14m 28s
🪲 Godot CPP / Build and test Godot CPP	6m 42s
	5h 58m 15s

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