BUG URL concat with Requirements::set_suffix_requirements(false) (fixes #8265)

Was breaking requirements with GET params because they were
concatenated starting with an ampersand rather than a questionmark.
Refactored to use http_build_query() and parse_str() as
more robust solutions for this problem.
Decode TinyMCE JS path before passing to Requirements

Requirements::javascript() expects unescaped paths,
otherwise it messes up the query re-assembly (see #8265)
Merge pull request #1206 from chillu/pulls/requirements-parseargs

Fixed Requirements::path_for_file()