API to retrieve opcode operand and extended_value meaning View as Markdown

I've fixed few issues reported by Bob.

Hi,

Please review the PR (for master only).
It adds an API call to get information about opcode operand and
extended_value meaning. This API should be useful for phpdbg, xdebug and
others.
Once these extension switch to new API, they will support most new opcodes
out of the box.

https://github.com/php/php-src/pull/1610

Comments and additional ideas are welcome.

Thanks. Dmitry.