Renaming WebGPU to WebGPU-SPIRV (ala Metal-SPIRV). (#16586)

This is more consistent and lets us separate the device (WebGPU) from
the compilation path that targets it (SPIR-V to WGSL). This also sets us
up for another path to lowering to WGSL in the future (same reason we
have Metal-SPIRV).
diff --git a/compiler/setup.py b/compiler/setup.py
index 85b99f3..9d99e9a 100644
--- a/compiler/setup.py
+++ b/compiler/setup.py
@@ -258,7 +258,7 @@
             "-DCMAKE_PLATFORM_NO_VERSIONED_SONAME=ON",
             "-DPython3_EXECUTABLE={}".format(sys.executable),
             "-DCMAKE_BUILD_TYPE={}".format(cfg),
-            # TODO(scotttodd): include IREE_TARGET_BACKEND_WEBGPU here (and in env)
+            # TODO(scotttodd): include IREE_TARGET_BACKEND_WEBGPU_SPIRV here (and in env)
             get_env_cmake_option("IREE_ENABLE_CPUINFO", "ON"),
             get_env_cmake_option("IREE_TARGET_BACKEND_ROCM", "ON"),
             get_env_cmake_option("IREE_ENABLE_LLD", "OFF"),