Add `@export_tool_button` annotation for easily creating inspector buttons. #40595

Job	Run time
📊 Static checks / Code style, file formatting, and docs	28s
🍎 macOS / Editor (target=editor, tests=yes)	25m 12s
🤖 Android / Editor (target=editor)	23m 3s
🍎 macOS / Template (target=template_release, tests=yes)	4m 25s
🤖 Android / Template arm32 (target=template_release, arch=arm32)	3m 0s
🍏 iOS / Template (target=template_release)	1m 40s
🤖 Android / Template arm64 (target=template_release, arch=arm64)	2m 57s
🐧 Linux / Editor w/ Mono (target=editor)	37m 28s
🐧 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)	41m 9s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	22m 27s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	31m 7s
🌐 Web / Template w/o threads (target=template_release, threads=no)	23m 16s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	30m 42s
🏁 Windows / Editor (target=editor, tests=yes)	48m 52s
🐧 Linux / Template w/ Mono (target=template_release, tests=yes)	23m 5s
🏁 Windows / Editor w/ clang-cl (target=editor, tests=yes, use_llvm=yes)	39m 50s
🐧 Linux / Minimal template (target=template_release, tests=yes, everything disabled)	53s
🏁 Windows / Template (target=template_release, tests=yes)	33m 13s
🪲 Godot CPP / Build and test Godot CPP	8m 38s
	6h 41m 25s

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