- #4083
- `<link>` tag helper did not HTML encode `href` values in fallback elements
- `<script>` tag helper did not correctly encode any attribute value in fallback elements
- e.g. double quotes in literal strings would slip through
- only needed to change one existing unit test (!!); so added a bunch
nit: use `Process()`, not `ProcessAsync()` in `<script>` tag helper tests
