chore(editorcfg): keep eol whitespace in tests (#11007)

Keep editor from removing trailing whitespace in format test files and
snapshots.

.editorconfig

@@ -14,3 +14,9 @@ insert_final_newline = false
 
 [website/blog/*.md]
 trim_trailing_whitespace = false
+
+[tests/{**/__snapshots__/*, tests/format/**/*}]
+trim_trailing_whitespace = false
+
+[tests/format/**/jsfmt.spec.js]
+trim_trailing_whitespace = true