Refactor folder (#10475)

Move many third-party components' source codes from the src folder to a new folder called deps_src. The goal is to make the code structure clearer and easier to navigate.

deps_src/admesh/CMakeLists.txt

@@ -0,0 +1,22 @@
+cmake_minimum_required(VERSION 3.13)
+project(admesh)
+
+add_library(admesh STATIC
+    connect.cpp
+    normals.cpp
+    shared.cpp
+    stl.h
+    stl_io.cpp
+    stlinit.cpp
+    util.cpp
+)
+
+target_include_directories(admesh PUBLIC
+    ${CMAKE_CURRENT_SOURCE_DIR}
+    ${CMAKE_CURRENT_SOURCE_DIR}/..
+)
+
+target_link_libraries(admesh 
+    PRIVATE boost_headeronly
+    PUBLIC eigen
+)