More precise document.close() injection

[ikreymer]

• follow up to #138, #141
• ensure text/* scripts do not get document.close() injection (fixes rewriting of: https://www.gigharborfire.org/contact-us/contact-form/)
• also ensure document.close is injected into scripts that have a top-level document.write (fixes rewriting of: https://developer.ninjaforms.com/codex/custom-field-templates/)
• fixes webrecorder/wombat#131

test: disable testBlockloaders by renaming to _testBlockloaders