Fix header errors when parsed standalone

[iluuu1994]

This is annoying for multiple reasons:

1. LSPs can show many errors for these files.
2. LSP can stop parsing these files completely if there are too many errors, resulting in spotty LSP features.

On my machine, two debug build without ccache took 55s/56s for master, and 56s/56s for this branch, so it does not seem like it changed significantly.

[dstogov]

I don't see anything bad.
I'm not sure why do you need a separate header for zend_result...

[Girgias]

LGTM

[iluuu1994]

I'm not sure why do you need a separate header for zend_result...

It reduced a few imports of zend_types.h. I reverted the change and include zend_types.h instead.

[TimWolla]

I'm in favor, but would like to point out this RFC: https://wiki.php.net/rfc/include_cleanup and this PR: #10609.

I believe there should be a more systematic approach than just making a few changes here and there when one notices the issues.

[iluuu1994]

I'm aware of the RFC, but since it was declined, it doesn't seem sincere to make the same changes again. Another proposal might be more successful now, with less drama.

[MaxKellermann]

This PR adds forward declarations which was an idea I proposed in https://wiki.php.net/rfc/include_cleanup but was rejected by the majority of PHP developers, including @dstogov - now I wonder why he agreed with this PR ... ?