Add WebGPU Backend w/ Dawn Support (#3838)

vendor/webgpu.cmake

@@ -0,0 +1,18 @@
+# WebGPU implementation configuration
+# This file handles the integration of either Dawn or wgpu
+
+set(MLN_WEBGPU_IMPL "dawn" CACHE STRING "WebGPU backend implementation (dawn or wgpu)")
+set_property(CACHE MLN_WEBGPU_IMPL PROPERTY STRINGS dawn wgpu stub)
+
+if(MLN_WITH_WEBGPU)
+    if(MLN_WEBGPU_IMPL STREQUAL "dawn")
+        message(STATUS "Using Dawn as WebGPU backend")
+
+    elseif(MLN_WEBGPU_IMPL STREQUAL "wgpu")
+        message(FATAL_ERROR "Using wgpu as WebGPU backend is not implemented yet")
+
+    else()
+        message(FATAL_ERROR "MLN_WEBGPU_IMPL can take values \"dawn\" or \"wgpu\"")
+
+    endif()
+endif()