Add sane editorconfig settings (#3051)

- UNIX line endings
- utf8
- newline at end of file
- trim trailing whitespace

.editorconfig

@@ -7,6 +7,15 @@ root = true
 indent_style = tab
 indent_size = 4
 tab_width = 4
+end_of_line = lf
+insert_final_newline = true
+charset = utf-8
+trim_trailing_whitespace = true
+
+# Don't change test output files
+[*.out]
+insert_final_newline = unset
+trim_trailing_whitespace = unset
 
 [*.sql]
 indent_style = space