Fix ImTextureID type #457

Job	Run time
clang-format	32s
Windows MSVC Shared Release	1m 52s
Windows MSVC Shared Debug	1m 42s
Windows MSVC Static Release	3m 40s
Windows MSVC Static Debug	3m 33s
Windows ClangCL Shared Release	3m 34s
Windows ClangCL Shared Debug	3m 18s
Windows ClangCL Static Release	4m 47s
Windows ClangCL Static Debug	3m 9s
Windows Clang Shared Release	2m 5s
Windows Clang Shared Debug	1m 55s
Windows Clang Static Release	2m 31s
Windows Clang Static Debug	2m 17s
Linux GCC Shared Release	47s
Linux GCC Shared Debug	41s
Linux GCC Static Release	1m 17s
Linux GCC Static Debug	1m 11s
Linux Clang Shared Release	55s
Linux Clang Shared Debug	50s
Linux Clang Static Release	1m 26s
Linux Clang Static Debug	1m 27s
macOS Clang Shared Release	1m 9s
macOS Clang Shared Debug	1m 18s
macOS Clang Static Release	1m 0s
macOS Clang Static Debug	53s
	47m 49s

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