Use `_v` shorthand for type traits and `if constexpr` where appropriate #21469

Job	Run time
📊 Static checks / Code style, file formatting, and docs	28s
🤖 Android / Template (target=template_release)	24m 30s
🍏 iOS / Template (target=template_release)	15m 0s
🍎 macOS / Editor (target=editor, tests=yes)	23m 40s
🍎 macOS / Template (target=template_release)	29m 5s
🏁 Windows / Editor (target=editor, tests=yes)	36m 33s
🐧 Linux / Editor w/ Mono (target=editor)	30m 13s
🏁 Windows / Template (target=template_release)	25m 37s
🐧 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)	27m 9s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	18m 6s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	27m 30s
🌐 Web / Template w/o threads (target=template_release, threads=no)	18m 16s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	24m 59s
🐧 Linux / Template w/ Mono (target=template_release)	19m 13s
🐧 Linux / Minimal template (target=template_release, everything disabled)	14m 2s
🪲 Godot CPP / Build and test Godot CPP	6m 45s
	5h 41m 6s

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