[Developers] Standardize on `PF2GameplayAbilityUtilities::GetTag()` or `FGameplayTag::RequestGameplayTag()`

[GuyPaddock]

As a Developer maintaining OpenPF2, I'd like it if C++ code that works with gameplay tags would standardize on using either PF2GameplayAbilityUtilities::GetTag() or FGameplayTag::RequestGameplayTag() but not both so that code behaves uniformly and is easier to maintain.

Conditions of Acceptance

Given I'm looking at C++ code that needs to request a gameplay tag:

1. I'd expect all the code to use either PF2GameplayAbilityUtilities::GetTag() or FGameplayTag::RequestGameplayTag().
2. I'd expect to not find any code using the opposite (outside of the utility method upon which we've standardized).