Backends, Examples: WGPU: wip refactor. (8381)

Rebased and squashed 47 commits.
- ImGui WebGPU examples: removed swap-chain in favor of surfaceConfigure (8191)
- New SDL2 WGPU example
- Code optimization: removed the redundancies of assignment
- Changes: ImGui code style - Lambdas RequestAdapter and RequestDevice callbacks declarated as signature - Validation Layer callbacks moved from lambdas to standard functions
- Same changes of GLFW example: ImGui code style - Lambdas RequestAdapter and RequestDevice callbacks declarated as signature - Validation Layer callbacks moved from lambdas to standard functions
- Scrollbars inhibition
- Use of new direct CreateDevice function (w/o callback), added release of all resources used (not present in original example)
- If the O.S. is Linux/Unix check if Wayland is the current active session and set DAWN_USE_WAYLAND=ON option (otherwise is always OFF)
- example_glfw_wgpu: removed all workarounds
- example_sdl2_wgpu: same style and functionality as GLFW example
- sdl2wgpu tool to acquire surfaceDescriptor via SDL_syswm and to pass to wgpuInstanceCreateSurface to create WGPU Surface
- css style to avoid the scrollbar
- added `chek_surface_texture_status` function to check the `WGPUSurfaceTexture .status` and recreate the `Surface` in case of "not optimal" (bad) status.
- Changed comment reference to `emwgpudawn` an EMSCRIPTEN WGPU binding maintained by Google
- Adaptation to the last Google DAWN commit (1411699ba)
Adaptation to the last EMSCRIPTEN 4.0.10, using new "--use-port=emdawnwebgpu" compiler/linker flag
- Support for EMSCRIPTEN >= 4.0.10 (using "--use-port=emdawnwebgpu") and NEW support for WGPU-Native
- Finalized the support of WGPU-Native for MacOS and minimal code adjustment
- WebGPU examples - DAWN / WGPU native and EMSCRIPTEN - for GLFW/SDL2/SDL3 frameworks
- "index.html" no more necessary (now the common one is used), "sdl2wgpu.cpp" It has been moved and renamed (sdl2_wgpu.c), "sdl2wgpu.h" no more necessary
- added procedure for using CMake
- added procedure for using CMake
- Updated example_sdl3_wgpu build procedure for EMSCRIPTEN
- WGPU+GLFW: Helper to create a WebGPU surface for Native application. Used only with WGPU-Native SDK: DAWN-Native already has a built-in function
- WGPU+SDL2: helper to create a WebGPU surface (exclusively!) for Native/Desktop applications and available only together with WebGPU/WGPU backend
- WGPU+SDL3: helper to create a WebGPU surface (exclusively!) for Native/Desktop applications and available only together with WebGPU/WGPU backend
- WebGPU Helper functions and differentiation between the 4 compilation methods (via defines): Google DAWN (Native/Emscripten) / WGPU (Native/EMscripten)
- example_glfw_wgpu: ImGui_ImplGLFW_CreateWGPUSurface_Helper (new helper function in imgui_impl_glfw backend), check status and error callback functions in imgui_impl_wgpu backend
- example_sdl2_wgpu: ImGui_ImplSDL2_CreateWGPUSurface_Helper (new helper function in imgui_impl_sdl2 backend), check status and error callback functions in imgui_impl_wgpu backend
- example_sdl3_wgpu: ImGui_ImplSDL3_CreateWGPUSurface_Helper (new helper function in imgui_impl_sdl3 backend), check status and error callback functions in imgui_impl_wgpu backend
- Functions ImGui_ImplXXXX_CreateWGPUSurface_Helper were inserted into imgui_impl_xxxx (xxxx = GLFW / SDL2 / SDL3), and initialization has been integrated into every example: no more necessary, removed

backends/imgui_impl_sdl3.h

@@ -44,4 +44,10 @@ IMGUI_IMPL_API bool     ImGui_ImplSDL3_ProcessEvent(const SDL_Event* event);
 enum ImGui_ImplSDL3_GamepadMode { ImGui_ImplSDL3_GamepadMode_AutoFirst, ImGui_ImplSDL3_GamepadMode_AutoAll, ImGui_ImplSDL3_GamepadMode_Manual };
 IMGUI_IMPL_API void     ImGui_ImplSDL3_SetGamepadMode(ImGui_ImplSDL3_GamepadMode mode, SDL_Gamepad** manual_gamepads_array = nullptr, int manual_gamepads_count = -1);
 
+// SDL3 helper to create a WebGPU surface for Native/Desktop applications: available only with WebGPU/WGPU backend
+#if defined(IMGUI_IMPL_WEBGPU_BACKEND_WGPU) || defined(IMGUI_IMPL_WEBGPU_BACKEND_DAWN) && !defined(__EMSCRIPTEN__)
+#include <webgpu/webgpu.h>
+WGPUSurface ImGui_ImplSDL3_CreateWGPUSurface_Helper(WGPUInstance instance, SDL_Window* window);
+#endif
+
 #endif // #ifndef IMGUI_DISABLE