Update deprecated methods for unity 6

[lejean]

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[tigran-sargsyan-w]

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Hey, nice update 👍

From a quick look, the changes make sense for Unity 6:

• Swapping the deprecated ShaderUtil calls to shader.GetPropertyCount / GetPropertyType / GetPropertyName looks good and keeps the logic the same.
• Using the generic TreeView<int> / TreeViewItem<int> API matches the newer UnityEditor IMGUI TreeView API and keeps the rest of the code pretty clean.
• The ShaderPropertyFlags.NonModifiableTextureData check seems like the right replacement for the old IsShaderPropertyNonModifiableTexureProperty usage.

Only thing I’m wondering about is minimal Unity version support for this repo. If it’s still meant to support older versions, you might want some #if UNITY_... guards around the new APIs. If the plugin is moving fully to the newer versions, then this looks fine as-is.

Overall, this feels like a solid pass over the deprecated APIs 👌