Simplify (maybe) the imgui submodules

Use cimgui which avoids the copy-files-into-our-repo step

.gitmodules

@@ -1,3 +1,3 @@
-[submodule "imgui-sys/third-party/imgui"]
-	path = imgui-sys/third-party/imgui
-	url = https://github.com/ocornut/imgui
+[submodule "imgui-sys/third-party/cimgui"]
+	path = imgui-sys/third-party/cimgui
+	url = https://github.com/cimgui/cimgui.git

imgui-sys/build.rs

@@ -36,8 +36,8 @@ fn main() -> io::Result<()> {
     if std::env::var_os("CARGO_FEATURE_WASM").is_none() {
         // Check submodule status. (Anything else should be a compile error in
         // the C code).
-        assert_file_exists("third-party/cimgui.cpp")?;
-        assert_file_exists("third-party/imgui/imgui.cpp")?;
+        assert_file_exists("third-party/cimgui/cimgui.cpp")?;
+        assert_file_exists("third-party/cimgui/imgui/imgui.cpp")?;
 
         let mut build = cc::Build::new();
 

imgui-sys/include_all_imgui.cpp

@@ -2,11 +2,9 @@
 // allowing the optimizer to inline across separate object files (note that even
 // when rust is built with LTO, unless the steps are taken to allow cross-lang
 // LTO (tricky), the C/C++ code won't be LTOed).
-#include "./third-party/imgui/imgui.cpp"
-#include "./third-party/imgui/imgui_demo.cpp"
-#include "./third-party/imgui/imgui_draw.cpp"
-#include "./third-party/imgui/imgui_widgets.cpp"
-#include "./third-party/imgui/imgui_tables.cpp"
-#include "./third-party/cimgui.cpp"
-
-
+#include "./third-party/cimgui/imgui/imgui.cpp"
+#include "./third-party/cimgui/imgui/imgui_demo.cpp"
+#include "./third-party/cimgui/imgui/imgui_draw.cpp"
+#include "./third-party/cimgui/imgui/imgui_widgets.cpp"
+#include "./third-party/cimgui/imgui/imgui_tables.cpp"
+#include "./third-party/cimgui/cimgui.cpp"