Handle built-in shaders when closing scene #774

Job	Run time
📊 Static checks / Code style, file formatting, and docs	2m 46s
🤖 Android / Template (target=template_release)	27m 50s
🍎 macOS / Editor (target=editor, tests=yes)	28m 13s
🐧 Linux / Editor w/ Mono (target=editor)	33m 58s
🍎 macOS / Template (target=template_release)	17m 8s
🍏 iOS / Template (target=template_release)	29m 27s
🐧 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)	35m 16s
🌐 Web / Template (target=template_release)	20m 51s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	32m 11s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	26m 28s
🐧 Linux / Template w/ Mono (target=template_release)	22m 56s
🏁 Windows / Editor (target=editor, tests=yes)	41m 4s
🐧 Linux / Minimal template (target=template_release, everything disabled)	14m 35s
🏁 Windows / Template (target=template_release)	29m 23s
🪲 Godot CPP / Build and test Godot CPP	6m 49s
	6h 8m 55s

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