Squashed 'external/imgui/imgui/' content from commit d4ddc46e7

git-subtree-dir: external/imgui/imgui
git-subtree-split: d4ddc46e7773e9a9b68f965d007968f35ca4e09a

.editorconfig

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+# 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-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
+root = true
+
+# Default settings:
+# Use 4 spaces as indentation
+[*]
+indent_style = space
+indent_size = 4
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[imstb_*]
+indent_size = 3
+trim_trailing_whitespace = false
+
+[Makefile]
+indent_style = tab
+indent_size = 4