Escaping issue in shortcodes

### Steps to Reproduce
- Have a Gutenberg paragraph block with shortcode:
`[code lang="php"]if(a && b) {}[/code]`
*— special characters are escaped for this in the stored post content*
- Syntaxhighlighter also escapes this and renders `if(a && b) {}`

### PHP / WordPress / SyntaxHighlighter Evolved version
- Issue is present in 3.6.0 even after the fixes, which looks like only fixed it for code blocks

### Context / Source

See p7H4VZ-3dm-p2

Reproduce the `[code lang="php"]` shortcode in a Gutenberg paragraph using `if(a && b) {}` and compare the stored post content with the rendered output. Trace the shortcode's escaping path first; done means the rendered code shows `&&` once rather than double-escaped `&`.

Written by the indexing model from the issue text.