Replace .NET detection code with `ClassDB::class_exists("CSharpScript")`. #35419

Job	Run time
📊 Static checks / Code style, file formatting, and docs	32s
🍏 iOS / Template (target=template_release)	1m 58s
🍎 macOS / Editor (target=editor, tests=yes)	5m 16s
🐧 Linux / Editor w/ Mono (target=editor)	4m 54s
🤖 Android / Editor (target=editor)	5m 1s
🍎 macOS / Template (target=template_release)	3m 26s
🐧 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)	16m 59s
🤖 Android / Template arm32 (target=template_release, arch=arm32)	3m 31s
🤖 Android / Template arm64 (target=template_release, arch=arm64)	3m 43s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	11m 32s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	6m 30s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	10m 30s
🏁 Windows / Editor (target=editor, tests=yes)	9m 55s
🌐 Web / Template w/o threads (target=template_release, threads=no)	6m 52s
🐧 Linux / Template w/ Mono (target=template_release)	1m 43s
🏁 Windows / Template (target=template_release)	8m 49s
🐧 Linux / Minimal template (target=template_release, everything disabled)	2m 19s
🪲 Godot CPP / Build and test Godot CPP	7m 55s
	1h 51m 25s

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