Migrate SKIPIF -> EXTENSIONS (#7138)

This is an automated migration of most SKIPIF extension_loaded checks.

Declare tentative return types for ext/session (#7005)

Fix #79413: session_create_id() fails for active sessions

The comment on `PS_VALIDATE_SID_FUNC(files)` is very clear that the
function is supposed to return `SUCCESS` if the session alre

Fix #79413: session_create_id() fails for active sessions

The comment on `PS_VALIDATE_SID_FUNC(files)` is very clear that the
function is supposed to return `SUCCESS` if the session already exists.
So to detect a collision, we have to check for `SUCCESS`, not
`FAILURE`.

We also fix the wrong condition in session_regenerate_id() as well.

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Fix #79091: heap use-after-free in session_create_id()

If the `new_id` is released, we must not use it again.