Add the basic developer's documentation for the Wasm port #12950

Job	Run time
Code style check / Code style check	9s
IWYU / IWYU	3m 18s
SonarCloud Analyzer / SonarCloud Analyzer	0s
CodeChecker / CodeChecker	32m 37s
MSVC / MSVC (SDL2 x86)	3m 55s
MSVC / MSVC (SDL2 x64)	4m 16s
CMake / CMake (Windows SDL2)	7m 24s
CMake / CMake (Linux SDL2)	2m 10s
Android / Android	9m 37s
CMake / CMake (macOS SDL2)	1m 38s
CMake / CMake (macOS SDL2 App Bundle)	2m 46s
Make / Make (Emscripten)	3m 56s
Make / Make (Linux x86-64 SDL2 Release)	2m 54s
Make / Make (Linux x86-64 SDL2 Debug)	3m 7s
Make / Make (Nintendo Switch)	3m 9s
Make / Make (Linux ARM64 SDL2 Release)	5m 2s
Make / Make (PS Vita)	9m 30s
Make / Make (Linux ARM64 SDL2 Debug)	4m 44s
Make / Make (macOS SDL2)	3m 9s
Make / Make (macOS SDL2 App Bundle)	1m 31s
	1h 44m 52s

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