kernel: Add import blocks function to C header

Add `btck_import_blocks` to import block data and rebuild indexes. The
function can either reindex all existing block files if the indexes were
previously wiped through the chainstate manager options, or import
blocks from specified file paths.

src/kernel/bitcoinkernel_wrapper.h

@@ -690,6 +690,20 @@ public:
     {
     }
 
+    bool ImportBlocks(const std::span<const std::string> paths)
+    {
+        std::vector<const char*> c_paths;
+        std::vector<size_t> c_paths_lens;
+        c_paths.reserve(paths.size());
+        c_paths_lens.reserve(paths.size());
+        for (const auto& path : paths) {
+            c_paths.push_back(path.c_str());
+            c_paths_lens.push_back(path.length());
+        }
+
+        return btck_chainstate_manager_import_blocks(get(), c_paths.data(), c_paths_lens.data(), c_paths.size()) == 0;
+    }
+
     bool ProcessBlock(const Block& block, bool* new_block)
     {
         int _new_block;