Move duplicated imatrix code into single common imatrix-loader.cpp (#22445)

* Deduplicate imatrix loading code

* Add back LLAMA_TRACE, early exit on quantize missing metadata

common/imatrix-loader.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <cstdint>
+#include <map>
+#include <string>
+#include <vector>
+
+inline constexpr const char * LLM_KV_IMATRIX_DATASETS    = "imatrix.datasets";
+inline constexpr const char * LLM_KV_IMATRIX_CHUNK_COUNT = "imatrix.chunk_count";
+inline constexpr const char * LLM_KV_IMATRIX_CHUNK_SIZE  = "imatrix.chunk_size";
+
+struct common_imatrix_entry {
+    std::vector<float>   sums;
+    std::vector<int64_t> counts;
+};
+
+struct common_imatrix {
+    std::map<std::string, common_imatrix_entry> entries;
+    std::vector<std::string> datasets;
+    int32_t chunk_count    = 0;
+    int32_t chunk_size     = 0;
+    bool    is_legacy      = false;
+    bool    has_metadata   = false;
+};
+
+bool common_imatrix_load(const std::string & fname, common_imatrix & imatrix);