Always allocate linear memory using mmap (#3052)

With this approach we can omit using memset() for the newly allocated memory
therefore the physical pages are not being used unless touched by the program.

This also simplifies the implementation.

core/iwasm/common/wasm_memory.h

@@ -42,6 +42,14 @@ void
 wasm_runtime_set_enlarge_mem_error_callback(
     const enlarge_memory_error_callback_t callback, void *user_data);
 
+void
+wasm_deallocate_linear_memory(WASMMemoryInstance *memory_inst);
+
+int
+wasm_allocate_linear_memory(uint8 **data, bool is_shared_memory,
+                            uint64 num_bytes_per_page, uint64 init_page_count,
+                            uint64 max_page_count, uint64 *memory_data_size);
+
 #ifdef __cplusplus
 }
 #endif