Add Webgpu backend (#2132)

* WebGPU first draft (shaderc bin version 8)

* WebGPU scripts

scripts/genie.lua

@@ -3,6 +3,11 @@
 -- License: https://github.com/bkaradzic/bgfx#license-bsd-2-clause
 --
 
+newoption {
+	trigger = "webgpu",
+	description = "Enable webgpu experimental renderer.",
+}
+
 newoption {
 	trigger = "with-amalgamated",
 	description = "Enable amalgamated build.",
@@ -162,6 +167,12 @@ if not os.isdir(BX_DIR) or not os.isdir(BIMG_DIR) then
 	os.exit()
 end
 
+if _OPTIONS["webgpu"] then
+	DAWN_DIR   = os.getenv("DAWN_DIR")
+
+	_OPTIONS["with-windows"] = "10.0"
+end
+
 dofile (path.join(BX_DIR, "scripts/toolchain.lua"))
 if not toolchain(BGFX_BUILD_DIR, BGFX_THIRD_PARTY_DIR) then
 	return -- no action specified
@@ -214,6 +225,10 @@ function exampleProjectDefaults()
 		"bx",
 	}
 
+	if _OPTIONS["webgpu"] then
+		usesWebGPU()
+	end
+
 	if _OPTIONS["with-sdl"] then
 		defines { "ENTRY_CONFIG_USE_SDL=1" }
 		links   { "SDL2" }