Added type_all() function

[joente]

Description

Currently, we need mod_type(...) with action all to get all instances of a given type. It would be useful to have a function which returns with a set of all instances.

Benefits of having the type_all function:

• mod_type creates an event, type_all does not.
• mod_type indicates a change to the collection structure, type_all does not.
• mod_type requires a callback, type_all is just a set and can be used as preferred.

Especially the second argument is useful, as we want to implement a migration history in the future where we want calls to mod_type to be marked as a change to the collection structure.

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• Test collection functions

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• New and existing unit tests pass locally with my changes