UDIMs uv_scale and uv_offset shader uniform parameters not exposed for tiledimage and UsdUVTexture nodes

Looking at the current implementation of UDIMs there seems to be two choices:

1- Magic uv_scale and uv_offset ports appearing on top-level shader interface keyed to the `image` node name.
2- Global `UDIM_SET_PROPERTY` declaration affecting every single image in the MaterialX document.

Whenever an `image` node is hidden in a nodegraph, the uv_scale and uv_offset attributes do not propagate to the final shader interface, requiring option 2 to be used.

I would like to suggest expanding option 1, but this requires propagating scale/offset inputs thru parent nodegraph interfaces. Since I will be mentioning changes that will break the shader ABI this will be done only if explicitly requested by the DCC dev by setting a new ShaderGen option.

Let's take an arbitrary NodeGraph implementing the following NodeDef as an example:
```xml






```

The NodeGraph implementation of this definition will use two image nodes connected to the `rustfile` and `diffusefile` inputs. Could be other types of NodeGraph-implemented image nodes because the algo must be recursive to completely exit all the NodeGraph layers.

Let's say we are doing shadergen for a material using one `rustedimage` node called `Rusty1`.

We dig inside and end up at some point calling `HwImageNode::addInputs()` for the image nodes handling the `rustfile`.
1- The image ShaderNode being processed gets two new inputs, named `file_uv_scale` and `file_uv_offset`
2- We then look at the parent NodeGraph, find out that input `rustfile` is connected to the `file` input of the ShaderNode being processed, so we add `rustfile_uv_scale` connected to `file_uv_scale` and `rustfile_uv_offset` connected to `file_uv_offset`

Similarly we end up with `diffusefile_uv_scale` and `diffusefile_uv_offset` for the other image ShaderNode connected to the `diffusefile` filename input. Now you see why we use the name of the filename port as prefix.

When shadergen is done, I expect 4 new shader inputs to appear on the final shader ABI, matching the filename inputs. The shadergen will prefix these uniform parameters with the node name, so we end up with:
- `Rusty1_rustfile`
- `Rusty1_rustfile_uv_scale`
- `Rusty1_rustfile_uv_offset`
- `Rusty1_diffusefile`
- `Rusty1_diffusefile_uv_scale`
- `Rusty1_diffusefile_uv_offset`

So when we feed texture data to this shader, we can find the right `uv_scale` and `uv_offset` attributes for each texture file encountered by simply appending to the filename input we are currently resolving, and we can expect those scale and offset values to reach the `mx_image` function call in the shader code.

Does this make sense?

Start at HwImageNode::addInputs() and trace how parent NodeGraph interfaces are propagated through recursive NodeGraph layers. Review the proposed ShaderGen option and the existing UDIM handling around uv_scale and uv_offset. Done means matching scale and offset shader inputs reach the final shader ABI and the mx_image call for each filename input.

Written by the indexing model from the issue text.