tools: enable block-spacing rule in .eslintrc

Enable rule to enforce consistent use of space between the `{` and `}`
that surround a code block and the code block itself. This enforces via
linting the de facto standard in the code base.

PR-URL: #10377
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Julian Duque <julianduquej@gmail.com>

.eslintrc

@@ -76,6 +76,7 @@ rules:
 
   # Stylistic Issues
   # http://eslint.org/docs/rules/#stylistic-issues
+  block-spacing: 2
   brace-style: [2, 1tbs, {allowSingleLine: true}]
   comma-spacing: 2
   comma-style: 2