upgrade to docking imgui 1.90.0 (Kenix3#374)

ocornut/imgui@ce0d0ac

changes we currently have from the version of upstream imgui we're based on briaguya-ai/imgui@f077471

extern/ImGui/.editorconfig

@@ -1,7 +1,11 @@
 # See http://editorconfig.org to read about the EditorConfig format.
 # - In theory automatically supported by VS2017+ and most common IDE or text editors.
-# - In practice VS2019 stills gets trailing whitespaces wrong :(
-#   - Suggest install to trim whitespaces: https://marketplace.visualstudio.com/items?itemName=MadsKristensen.TrailingWhitespaceVisualizer
+# - In practice VS2019-VS2022 stills don't trim trailing whitespaces correctly :(
+#   - Suggest installing this to trim whitespaces:
+#      GitHub https://github.com/madskristensen/TrailingWhitespace
+#      VS2019 https://marketplace.visualstudio.com/items?itemName=MadsKristensen.TrailingWhitespaceVisualizer
+#      VS2022 https://marketplace.visualstudio.com/items?itemName=MadsKristensen.TrailingWhitespace64
+#     (in spite of its name doesn't only visualize but also trims)
 #   - Alternative for older VS2010 to VS2015: https://marketplace.visualstudio.com/items?itemName=EditorConfigTeam.EditorConfig
 
 # top-most EditorConfig file

extern/ImGui/.github/FUNDING.yml

@@ -0,0 +1 @@
+custom: ['https://github.com/ocornut/imgui/wiki/Sponsors']

extern/ImGui/.github/issue_template.md

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+(Click "Preview" above ^ to turn URL into clickable links)
+
+1. FOR FIRST-TIME USERS PROBLEMS COMPILING/LINKING/RUNNING or LOADING FONTS,  please use [GitHub Discussions](https://github.com/ocornut/imgui/discussions). EVERYTHING ELSE CAN BE POSTED HERE!
+
+2. PLEASE CAREFULLY READ: [FAQ](https://github.com/ocornut/imgui/blob/master/docs/FAQ.md)
+
+3. PLEASE CAREFULLY READ: [Contributing Guidelines](https://github.com/ocornut/imgui/blob/master/docs/CONTRIBUTING.md)
+
+4. PLEASE MAKE SURE that you have: read the FAQ; explored the contents of `ShowDemoWindow()` including the Examples menu; searched among Issues; used your IDE to search for keywords in all sources and text files; and read the links above.
+
+5. Be mindful that messages are being sent to the e-mail box of "Watching" users. Try to proof-read your messages before sending them. Edits are not seen by those users.
+
+6. Delete points 1-6 and PLEASE FILL THE TEMPLATE BELOW before submitting your issue.
+
+Thank you!
+
+----
+
+_(you may also go to Demo>About Window, and click "Config/Build Information" to obtain a bunch of detailed information that you can paste here)_
+
+**Version/Branch of Dear ImGui:**
+
+Version: XXX
+Branch: XXX _(master/viewport/docking/etc.)_
+
+**Back-end/Renderer/Compiler/OS**
+
+Back-ends: imgui_impl_XXX.cpp + imgui_impl_XXX.cpp _(or specify if using a custom engine/back-end)_
+Compiler: XXX _(if the question is related to building or platform specific features)_
+Operating System: XXX
+
+**My Issue/Question:**
+
+XXX _(please provide as much context as possible)_
+
+**Screenshots/Video**
+
+XXX _(you can drag files here)_
+
+**Standalone, minimal, complete and verifiable example:** _(see https://github.com/ocornut/imgui/issues/2261)_
+```
+// Here's some code anyone can copy and paste to reproduce your issue
+ImGui::Begin("Example Bug");
+MoreCodeToExplainMyIssue();
+ImGui::End();
+```

extern/ImGui/.github/pull_request_template.md

@@ -0,0 +1,6 @@
+(Click "Preview" to turn any http URL into a clickable link)
+
+1. PLEASE CAREFULLY READ: [Contributing Guidelines](https://github.com/ocornut/imgui/blob/master/docs/CONTRIBUTING.md)
+
+2. Clear this template before submitting your PR.
+