Added SDL_IsMainThread() and SDL_RunOnMainThread() #511

Job	Run time
Create test plan	7s
level1 / Haiku	1m 57s
level2 / Android (Gradle)	2m 2s
level2 / Ubuntu 22.04	4m 22s
level2 / PowerPC	1m 49s
level2 / MacOS (Framework) (arm64)	3m 4s
level2 / Windows (MSVC, clang-cl x86)	5m 31s
level2 / Sony PlayStation 2	4m 49s
level2 / LoongArch64	3m 5s
level2 / tvOS (CMake & xcode)	1m 47s
level2 / Windows (MSVC, clang-cl x64)	5m 20s
level2 / Ubuntu 20.04	4m 2s
level2 / Sony PlayStation Vita (GLES w/ pib)	3m 5s
level2 / Sony PlayStation Portable	3m 45s
level2 / iOS (CMake & xcode)	1m 52s
level2 / NetBSD	2m 31s
level2 / Nintendo 3DS	1m 54s
level2 / Windows (msys2, clang64)	6m 13s
level2 / Android (Android.mk)	2m 23s
level2 / MacOS (GNU prefix)	3m 10s
level2 / Steam Linux Runtime (Sniper)	2m 46s
level2 / Windows (MSVC, ARM)	2m 54s
level2 / FreeBSD	2m 51s
level2 / Ubuntu 20.04 (Intel Compiler)	4m 58s
level2 / Windows (msys2, ucrt64)	8m 43s
level2 / GDK (MSVC, x64)	3m 40s
level2 / Windows (msys2, clang32)	7m 8s
level2 / Sony PlayStation Vita (GLES w/ PVR_PSP2)	3m 12s
level2 / PowerPC64	1m 54s
level2 / MacOS (Framework) (x64)	5m 29s
level2 / Emscripten	13m 26s
level2 / Windows (MSVC, x64)	5m 15s
level2 / Windows (msys2, mingw32)	8m 40s
level2 / Windows (msys2, mingw64)	8m 15s
level2 / RISC OS	1m 18s
level2 / Windows (MSVC, ARM64)	4m 0s
level2 / Android (CMake)	3m 54s
level2 / Windows (MSVC, x86)	5m 21s
level2 / Android (CMake, lean)	6m 31s
level2 / Ubuntu 20.04 (Intel oneAPI)	6m 31s
	2h 49m 34s

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