Add .editorconfig file (#1768)

See: https://editorconfig.org/

.editorconfig

@@ -0,0 +1,12 @@
+root = true
+
+[*]
+charset = utf-8
+indent_size = 4
+indent_style = space
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+
+[*.{yml,yaml}]
+indent_size = 2

.gitattributes

@@ -5,3 +5,4 @@
 /phpunit.xml.dist export-ignore
 /_config.yml export-ignore
 /UPGRADE.md
+/.editorconfig export-ignore