Create a working ImGui WebGL template project.

[zwcloud]

The basic OpenGL experimental demo based on new dotnet/runtime/mono/wasm is successful at 5d208f7.
And the next step is to fix WebGL port to run the ImGui demo on a brower.

[zwcloud]

But the performance is very possibly bad according to https://marcoscobena.com/?i=wave-engine-web-performance

Trying donet/runtimelab/NativeAOT-LLVM WebAssembly instead.

The basic OpenGL experimental demo based on new donet/runtimelab/NativeAOT-LLVM WebAssembly is successful at https://github.com/zwcloud/MinimalCSharpWasmWebGL-NativeAOT-LLVM

But the toolchain will fail when compiling ImGui.dll to wasm: there are bugs in NativeAOT-LLVM needed to be fixed.