[Fix] lua_content: Move PDF ligature substitutions from string unescape to text handler

[Fix] lua_content: Move PDF ligature substitutions from string unescape to text handler

StandardEncoding/MacRomanEncoding ligature substitutions (e.g. byte 0xAD -> 'ffl')
were applied to all PDF strings including /URI annotation values. This corrupted
soft hyphens (U+00AD) in URLs, preventing the URL parser from detecting zero-width
space obfuscation and setting the ZW_SPACES flag.

Move ligature substitutions to text_op_handler where they belong, so they only
apply to rendered text content (Tj/TJ operators), not to dictionary string values.