Vulkan: Remove texture allocation check

[kroketio]

During DEBUG_ENABLED (the default for Godot editor as distributed by Godot) a texture allocation check in texture_create_shared() causes foreign textures (those without tex_info->allocation) created by texture_create_from_extension() to fail, because such textures from external sources naturally lack the required allocation information.

godot/drivers/vulkan/rendering_device_driver_vulkan.cpp

Lines 1781 to 1783 in 61be39a

	#ifdef DEBUG_ENABLED
	ERR_FAIL_COND_V(!owner_tex_info->allocation.handle, TextureID());
	#endif

For example, a VkImage may be passed to texture_create_from_extension(), which is a function to handle incoming textures from external sources:

godot/servers/rendering/rendering_device.cpp

Lines 941 to 943 in 61be39a

	RID RenderingDevice::texture_create_from_extension(TextureType p_type, DataFormat p_format, TextureSamples p_samples, BitField<RenderingDevice::TextureUsageBits> p_usage, uint64_t p_image, uint64_t p_width, uint64_t p_height, uint64_t p_depth, uint64_t p_layers) {
	_THREAD_SAFE_METHOD_
	// This method creates a texture object using a VkImage created by an extension, module or other external source (OpenXR uses this).

But when the result is applied as albedo on a StandardMaterial3D, it will lead to the following error.

ERROR: Condition "!owner_tex_info->allocation.handle" is true. Returning: TextureID()
   at: texture_create_shared (drivers/vulkan/rendering_device_driver_vulkan.cpp:1600)
ERROR: Condition "!texture.driver_id" is true. Returning: RID()
   at: texture_create_shared (servers/rendering/rendering_device.cpp:906)
ERROR: Condition "!owner_tex_info->allocation.handle" is true. Returning: TextureID()
   at: texture_create_shared (drivers/vulkan/rendering_device_driver_vulkan.cpp:1600)
ERROR: Condition "!texture.driver_id" is true. Returning: RID()
   at: texture_create_shared (servers/rendering/rendering_device.cpp:906)

This PR removes the check, because for foreign textures (like VkImage) you only need a view, which texture_create_from_extension creates, and then just display the view, regardless of allocation information. In simple terms, this PR is necessary for external renderers to supply Godot with external textures.

[clayjohn]

I've requested a review from @RandomShaper as he added that check when doing a massive refactor of the RenderingDevice in #83452

[kroketio]

For context, this was also discussed July 10 in #rendering @ dev chat:

me:
ERROR: Condition "!owner_tex_info->allocation.handle" is true. Returning: TextureID()

dariasamo: 
@RandomShaper It seems like the driver validates whether a texture is not a slice 
by checking the allocation, which means you can't create a shared version or a 
slice out of an externally created texture. Should it check instead by storing some 
other flag?

randomshaper: 
To be fair, I know very little about that method.
If I recall correctly, it was added by mux213 to support certain VR needs.
Oh, you already mostly said that.
I have no idea how flexible it is in practice beyond its original purpose.

mux213:
Indeed, that function was added for XR so we can render to a texture created 
outside of the core of Godot. There are definitely limitations here as Godot 
does not control this texture. Can’t say for sure whether this situation 
should work, will have to take a closer look tomorrow.

dariosamo:
It should be fine, it's just a texture view.

[RandomShaper]

The check has the purpose of validating if the id corresponds to an actual texture owning the data, which is what RenderingDevice is expected to provide and so keep the driver free of having to resolve that itself.

Rather than removing the check, I'd suggest enrichening it so it also accounts for the cases of externally backed textures (i.e., created from extension):

• TextureInfo would get the following added below allocation:

  #ifdef DEBUG_ENABLED
  bool created_from_extension = false;
  #endif
  

• texture_create_from_extension() would do this last thing before the return:

  #ifdef DEBUG_ENBLED
  tex_info->created_from_extension = true;
  #endif
  

• The checks in both texture_create_shared() and texture_create_shared_from_slice() would change from
  ERR_FAIL_COND_V(!owner_tex_info->allocation.handle, TextureID());
  to
  ERR_FAIL_COND_V(!owner_tex_info->allocation.handle && !owner_tex_info->created_from_extension, TextureID());

As a final note, created_from_extension is the name that perfectly fits the current cases. If in the future another reason for a texture to be externally backed comes, we could just rename it to the more generic externally_backed.

[kroketio]

that indeed sounds like a better idea @RandomShaper
I opened a new PR over at #96860