style: add EditorConfig and format some files (#2106)

Add an EditorConfig to make sure editors know how to correctly edit and
save files. Also strip trailing whitespace in some files that don't need
it, as configured in the EditorConfig file.

.editorconfig

@@ -0,0 +1,40 @@
+root = true
+
+[*]
+indent_style = space
+indent_size = tab
+tab_width = 4
+insert_final_newline = true
+
+[*.xml]
+tab_width = 2
+trim_trailing_whitespace = true
+
+[*.php]
+insert_final_newline = false
+
+[*.css]
+insert_final_newline = false
+
+[*.py]
+# Otherwise Python language server complains
+trim_trailing_whitespace = true
+
+[*.xsl]
+trim_trailing_whitespace = true
+
+[*.md]
+trim_trailing_whitespace = true
+tab_width = 2
+
+[*.json]
+tab_width = 2
+trim_trailing_whitespace = true
+
+[*.{yml,yaml}]
+tab_width = 2
+
+[*.{c,cpp,cc,h,hpp}]
+indent_style = tab
+tab_width = 4
+trim_trailing_whitespace = true