UI text module refactor

[ickshonpe]

Objective

The measure_text_system and text_system systems don't do anything except iterate a query and then delegate to two other functions, create_text_measure and queue_text, respectively. This doesn't serve any purpose and just makes these systems harder to understand.

Solution

Flatten the module by moving the code from create_text_measure and queue_text into the systems and remove those functions.