Support extensions to provider generic helpers without having to override existing ones.

The documentation on [authoring helper functions](https://github.com/microsoft/ebpf-for-windows/blob/main/docs/eBpfExtensions.md#26-authoring-helper-functions) allows extensions to implement generic helpers. So extension X can implement a set of generic helpers {f} and a program of type Y may use it. Program Y will then be dependent on extension X for {f} and extension Y for program-specific helpers and hooks.
A possible solution could be to introduce a new NPI ID for generic helpers that any extension may choose to implement a provider for.

Start with docs/eBpfExtensions.md section 2.6, then trace the existing generic-helper provider and NPI model described in the issue. Define the API and compatibility requirements so an extension can add generic helpers without overriding existing ones, and confirm that programs can depend on those helpers alongside program-specific providers.

Written by the indexing model from the issue text.