Reduce code duplication in FileAccess #38258

Job	Run time
📊 Static checks / Code style, file formatting, and docs	31s
🍎 macOS / Editor (target=editor, tests=yes)	23m 36s
🐧 Linux / Editor w/ Mono (target=editor)	33m 21s
🍎 macOS / Template (target=template_release)	14m 53s
🐧 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 54s
🏁 Windows / Editor (target=editor, tests=yes)	42m 1s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	29m 23s
🏁 Windows / Editor w/ clang-cl (target=editor, tests=yes, use_llvm=yes)	36m 59s
🤖 Android / Editor (target=editor)	20m 50s
🍏 iOS / Template (target=template_release)	6m 49s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	26m 59s
🏁 Windows / Template (target=template_release)	27m 47s
🤖 Android / Template arm32 (target=template_release, arch=arm32)	12m 53s
🤖 Android / Template arm64 (target=template_release, arch=arm64)	12m 52s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	21m 2s
🐧 Linux / Template w/ Mono (target=template_release)	19m 12s
🌐 Web / Template w/o threads (target=template_release, threads=no)	21m 26s
🐧 Linux / Minimal template (target=template_release, everything disabled)	13m 2s
🪲 Godot CPP / Build and test Godot CPP	8m 13s
	6h 51m 43s

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