Changed GPU driver names to match renderer driver names

Fixes https://github.com/libsdl-org/SDL/issues/10650

src/gpu/d3d11/SDL_gpu_d3d11.c

@@ -6125,7 +6125,7 @@ tryCreateDevice:
 }
 
 SDL_GPUBootstrap D3D11Driver = {
-    "D3D11",
+    "direct3d11",
     SDL_GPU_DRIVER_D3D11,
     SDL_GPU_SHADERFORMAT_DXBC,
     D3D11_PrepareDriver,

src/gpu/d3d12/SDL_gpu_d3d12.c

@@ -8185,7 +8185,7 @@ static SDL_GPUDevice *D3D12_CreateDevice(bool debugMode, bool preferLowPower, SD
 }
 
 SDL_GPUBootstrap D3D12Driver = {
-    "D3D12",
+    "direct3d12",
     SDL_GPU_DRIVER_D3D12,
     SDL_GPU_SHADERFORMAT_DXIL,
     D3D12_PrepareDriver,

src/gpu/metal/SDL_gpu_metal.m

@@ -3974,7 +3974,7 @@ static SDL_GPUDevice *METAL_CreateDevice(bool debugMode, bool preferLowPower, SD
 }
 
 SDL_GPUBootstrap MetalDriver = {
-    "Metal",
+    "metal",
     SDL_GPU_DRIVER_METAL,
     SDL_GPU_SHADERFORMAT_MSL | SDL_GPU_SHADERFORMAT_METALLIB,
     METAL_PrepareDriver,

src/gpu/vulkan/SDL_gpu_vulkan.c

@@ -11788,7 +11788,7 @@ static SDL_GPUDevice *VULKAN_CreateDevice(bool debugMode, bool preferLowPower, S
 }
 
 SDL_GPUBootstrap VulkanDriver = {
-    "Vulkan",
+    "vulkan",
     SDL_GPU_DRIVER_VULKAN,
     SDL_GPU_SHADERFORMAT_SPIRV,
     VULKAN_PrepareDriver,