Add .vscode/settings.json compliant with Coding Style

As recommended in the Coding Style "Code editor" section:
https://developer.gimp.org/core/coding_style/#code-editor--integrated-development-environment-ide

.vscode/settings.json

@@ -0,0 +1,11 @@
+{
+  "C_Cpp.clang_format_fallbackStyle": "GNU",
+  "editor.rulers": [
+    80
+  ],
+  "editor.tabSize": 2,
+  "editor.renderControlCharacters": true,
+  "editor.renderWhitespace": "trailing",
+  "files.trimTrailingWhitespace": true,
+  "files.eol": "\n"
+}