Add missing descriptions to PrimitiveMesh and SoftBody3D #315

Job	Run time
📊 Static checks / Code style, file formatting, and docs	2m 38s
🍏 iOS / Template (target=template_release)	2m 38s
🍎 macOS / Editor (target=editor, tests=yes)	3m 41s
🤖 Android / Template (target=template_release)	3m 33s
🍎 macOS / Template (target=template_release)	3m 43s
🐧 Linux / Editor w/ Mono (target=editor)	2m 56s
🐧 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)	12m 34s
🌐 Web / Template (target=template_release)	1m 4s
🏁 Windows / Editor (target=editor, tests=yes)	7m 44s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	6m 9s
🏁 Windows / Template (target=template_release)	5m 39s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	5m 49s
🐧 Linux / Template w/ Mono (target=template_release)	55s
🐧 Linux / Minimal template (target=template_release, everything disabled)	44s
🪲 Godot CPP / Build and test Godot CPP	7m 12s
	1h 6m 59s

Provide feedback