shader: materialize image keys from proven GPU bitmap subsets

src/graphics/shader/recompiler/ir/ShaderIR.h

@@ -507,6 +507,8 @@ struct DescriptorSource {
 			uint32_t source = UINT32_MAX;
 			uint32_t stride = 0;
 			uint32_t offset = 0;
+			// Four DWORD bitmap words per record; set-bit ranks subtract from the last key.
+			bool bitset = false;
 			std::vector<std::pair<uint32_t, uint32_t>> byte_ranges;
 
 			bool operator==(const SelectorRead& other) const = default;
@@ -521,7 +523,7 @@ struct DescriptorSource {
 		bool     indexed_store = false;
 		uint32_t workgroup_axis  = UINT32_MAX;
 		Value    key_count;
-		// First selector index, or first descriptor key when no selector is present.
+		// First selector index, or first descriptor key for a direct or bitmap range.
 		Value                 selector_first;
 		Value    selector_mask;
 		std::vector<uint32_t> sources;