Rename ExprItemFrameSlot to reflect actual usage

[Fusezion]

Suggestion

Short and simple rename the ExprItemFrameSlot class into ExprItemSlot or ExprItemOfEntity, whatever one makes most sense

Why?

This classes syntax wasn't limited to just item frames since 2018 around the time of it's initial creation, retaining this class name is miss leading and hard to find.

Other

the PR #5604 will need to reflect theses changes as well when this is done

Agreement

• I have read the guidelines above and affirm I am following them with this suggestion.

[Fusezion]

additional note, unsure why but documentation site says return type is InventorySlot when it returns Slot and none of the actual return types extend InventorySlot they all use Slot

EDIT: I'm just dumb and forget skript uses InventorySlot as the classinfo name

[TheLimeGlass]

Planned to be done in #5601

[Fusezion]

Was completed in #5601