Super Admin Functions Network ID Support

[spenserhale]

Multisite installs that host multiple networks currently treat all super-admin functions as being tied to the primary network. This limits enterprise-scale setups (e.g., SaaS platforms that shard customers into separate networks)

The patch introduces first-class, backward-compatible support for a $network_id argument in four super-admin helpers, allowing each network to maintain an independent site_admins list while preserving legacy behavior.

Scope of Code Changes
The four helpers—get_super_admins(), is_super_admin(), grant_super_admin(), and revoke_super_admin()—now accept an optional $network_id parameter.
They now call get_network_option() / update_network_option() when a network ID is supplied; otherwise they keep using the current network (maintaining old behaviour).
Early returns and the global $super_admins override are preserved exactly as before.

Design and Back-Compatibility
Calling without $network_id still works exactly as today.
Calling with a specific $network_id now targets that network’s site_admins row.
If $GLOBALSsuper_admins? is defined, it still overrides everything and the new code short-circuits.
Plugin hooks (grant_super_admin, granted_super_admin, revoke_super_admin, revoked_super_admin) now receive $network_id as a second argument, but positional callbacks remain compatible.

All DocBlocks have been updated to describe the new parameter.
Hook signatures are extended but remain backward-compatible.
The change is fully transparent unless developers opt into the new argument.

Trac ticket: https://core.trac.wordpress.org/ticket/63536#ticket

Multisite installs that host multiple networks currently treat all super-admin functions as being tied to the primary network. This limits enterprise-scale setups (e.g., SaaS platforms that shard customers into separate networks)

The patch introduces first-class, backward-compatible support for a $network_id argument in four super-admin helpers, allowing each network to maintain an independent site_admins list while preserving legacy behavior.

Scope of Code Changes
The four helpers—get_super_admins(), is_super_admin(), grant_super_admin(), and revoke_super_admin()—now accept an optional $network_id parameter.
They now call get_network_option() / update_network_option() when a network ID is supplied; otherwise they keep using the current network (maintaining old behaviour).
Early returns and the global $super_admins override are preserved exactly as before.

Design and Back-Compatibility
Calling without $network_id still works exactly as today.
Calling with a specific $network_id now targets that network’s site_admins row.
If $GLOBALSsuper_admins? is defined, it still overrides everything and the new code short-circuits.
Plugin hooks (grant_super_admin, granted_super_admin, revoke_super_admin, revoked_super_admin) now receive $network_id as a second argument, but positional callbacks remain compatible.

All DocBlocks have been updated to describe the new parameter.
Hook signatures are extended but remain backward-compatible.
The change is fully transparent unless developers opt into the new argument.
Created new tests to test functionality.

Thanks for the PR! There are some coding standards issue to fix, see ​https://github.com/WordPress/wordpress-develop/pull/8921/files for the reported errors :)