Fix some `TileMap` debug drawing truncating to ints #19630

Job	Run time
📊 Static checks / Code style, file formatting, and docs	37s
🐧 Linux / Editor w/ Mono (target=editor)	5m 19s
🐧 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 57s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	9m 8s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	7m 11s
🤖 Android / Template (target=template_release)	28m 4s
🐧 Linux / Template w/ Mono (target=template_release)	2m 26s
🐧 Linux / Minimal template (target=template_release, everything disabled)	1m 53s
🍏 iOS / Template (target=template_release)	3m 13s
🌐 Web / Template (target=template_release)	3m 18s
🍎 macOS / Editor (target=editor, tests=yes)	4m 41s
🏁 Windows / Editor (target=editor, tests=yes)	9m 2s
🍎 macOS / Template (target=template_release)	3m 22s
🏁 Windows / Template (target=template_release)	30m 16s
🪲 Godot CPP / Build and test Godot CPP	6m 38s
	2h 12m 5s

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