Add .editorconfig

The same settings as in phpstan/phpstan

Author: vhenzl

.editorconfig

@@ -0,0 +1,27 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+charset = utf-8
+trim_trailing_whitespace = true
+
+[*.{php,phpt}]
+indent_style = tab
+indent_size = 4
+
+[*.{xml}]
+indent_style = tab
+indent_size = 4
+
+[*.{neon}]
+indent_style = tab
+indent_size = 4
+
+[*.{yaml,yml}]
+indent_style = space
+indent_size = 2
+
+[{composer.json}]
+indent_style = tab
+indent_size = 4