Add theme cache to the inspector #1366

Job	Run time
📊 Static checks / Code style, file formatting, and docs	1m 10s
🐧 Linux / Editor w/ Mono (target=editor)	38m 47s
🐧 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)	45m 48s
🍏 iOS / Template (target=template_release)	9m 55s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	35m 29s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	30m 12s
🍎 macOS / Editor (target=editor, tests=yes)	26m 4s
🤖 Android / Editor (target=editor)	24m 50s
🐧 Linux / Template w/ Mono (target=template_release)	24m 48s
🍎 macOS / Template (target=template_release)	21m 35s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	24m 16s
🤖 Android / Template arm32 (target=template_release, arch=arm32)	16m 24s
🐧 Linux / Minimal template (target=template_release, everything disabled)	15m 16s
🌐 Web / Template w/o threads (target=template_release, threads=no)	24m 52s
🤖 Android / Template arm64 (target=template_release, arch=arm64)	16m 46s
🏁 Windows / Editor (target=editor, tests=yes)	48m 32s
🏁 Windows / Template (target=template_release)	34m 38s
🪲 Godot CPP	0s
	7h 19m 22s

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