Introduce `Window` option to contain multiple `Viewports` with a focu… #344

Job	Run time
📊 Static checks / Code style, file formatting, and docs	3m 41s
🤖 Android / Template (target=template_release)	6m 28s
🍏 iOS / Template (target=template_release)	7m 29s
🌐 Web / Template w/ threads (target=template_release, threads=yes)	6m 9s
🌐 Web / Template w/o threads (target=template_release, threads=no)	6m 6s
🏁 Windows / Editor (target=editor, tests=yes)	44m 23s
🍎 macOS / Editor (target=editor, tests=yes)	28m 47s
🐧 Linux / Editor w/ Mono (target=editor)	13m 39s
🏁 Windows / Template (target=template_release)	7m 16s
🍎 macOS / Template (target=template_release)	3m 35s
🐧 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)	38m 52s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	34m 37s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	30m 15s
🐧 Linux / Template w/ Mono (target=template_release)	3m 50s
🐧 Linux / Minimal template (target=template_release, everything disabled)	3m 27s
🪲 Godot CPP / Build and test Godot CPP	7m 3s
	4h 5m 37s

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