Add missing descriptions for SliderJoint3D's `param` methods #19810

Job	Run time
📊 Static checks / Code style, file formatting, and docs	44s
🤖 Android / Template (target=template_release)	28m 23s
🍎 macOS / Editor (target=editor, tests=yes)	40m 18s
🍎 macOS / Template (target=template_release)	37m 28s
🍏 iOS / Template (target=template_release)	33m 15s
🐧 Linux / Editor w/ Mono (target=editor)	34m 12s
🌐 Web / Template (target=template_release)	19m 1s
🐧 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)	17m 59s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	6m 54s
🏁 Windows / Editor (target=editor, tests=yes)	41m 26s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	27m 45s
🏁 Windows / Template (target=template_release)	30m 10s
🐧 Linux / Template w/ Mono (target=template_release)	23m 47s
🐧 Linux / Minimal template (target=template_release, everything disabled)	14m 24s
🪲 Godot CPP / Build and test Godot CPP	6m 52s
	6h 2m 38s

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