Add depth function for spatial materials #48

Job	Run time
📊 Static checks / Code style, file formatting, and docs	24s
🤖 Android / Editor (target=editor)	21m 51s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	22m 38s
🌐 Web / Template w/o threads (target=template_release, threads=no)	23m 12s
🤖 Android / Template arm32 (target=template_release, arch=arm32)	14m 27s
🤖 Android / Template arm64 (target=template_release, arch=arm64)	14m 22s
🐧 Linux / Editor w/ Mono (target=editor)	36m 10s
🍎 macOS / Editor (target=editor, tests=yes)	24m 49s
🐧 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)	39m 4s
🍏 iOS / Template (target=template_release)	7m 44s
🍎 macOS / Template (target=template_release)	14m 49s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	31m 10s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	27m 36s
🐧 Linux / Template w/ Mono (target=template_release)	23m 4s
🏁 Windows / Editor (target=editor, tests=yes)	50m 9s
🐧 Linux / Minimal template (target=template_release, everything disabled)	14m 8s
🏁 Windows / Template (target=template_release)	39m 33s
🪲 Godot CPP	0s
	6h 45m 10s

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