Shader and Material stuff for "Material editor 2099"

[Exter-N]

⚠️ Due to some of the refactors, this PR is not backwards-compatible.

Shader Packages

• Rework the Items field into a Selectors dictionary to more closely match how the game handles it ;
• Add various stuff to manipulate shader selectors (which are calculated by Σ keys[m][n] * Pow(31, m + n)) ;
• Add a flag that allows determining after construction whether the shaders were disassembled.

Materials

Color Sets

• Fix the tile set assignment formula (though, due to rounding in the shader, it won't change anything in practice) ;
• Refactor ApplyDyeTemplate ;
• Add functions to turn the structures into Span<Half> ;
• Add logic to generate a ColorSet and/or a ColorDyeSet with sensible defaults from scratch ;
• Improve parsing (in some cases, the parser could mistake a file with color sets without rows but with lots of samplers and/or constants for a file with color sets with rows).

Miscellaneous

• Add functions to retrieve various structures from the material (constants, samplers, keys, color (dye) sets), generating them as needed ;
• Add a clone function that creates a deep copy of the loaded file, completely detached from the original ;
• Add a garbage collection function that finds and removes all unused and no-op elements from the file.
• Note: The "Clone + GC + Write" pattern is used in "Material editor 2099" to support a paradigm where, when the user switches shaders, the editor retains all the data for the previous shader in case the user changes their mind, or switches to a 3rd shader that uses some data the 1st used but not the 2nd, and discards everything superfluous on saving.