Add EditorConfig file

And recommend the EditorConfig extension.
The settings in .editorconfig are based on the files in the repo
and on .gitattributes

.editorconfig

+root = true
+
+[*]
+charset = utf-8
+indent_size = 2
+indent_style = space
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.js]
+end_of_line = lf

.vscode/extensions.json

 {
-  // See https://go.microsoft.com/fwlink/?LinkId=733558
+  // See https://go.microsoft.com/fwlink/?LinkId=827846
   // for the documentation about the extensions.json format
-  "recommendations": ["dbaeumer.vscode-eslint"]
+  "recommendations": [
+    "dbaeumer.vscode-eslint",
+    "editorconfig.editorconfig"
+  ]
 }