Error when multiple event-values are present for a default expression

[TheLimeGlass]

Description

Error when multiple event-values are present for a default expression.

This has been a common issue, where Skript silently selects the first event-value when grabbing a default expression.
For my example:

on throwing of an egg:
	send "test"

In theory Skript shouldn't know whether you want to message the egg or player in the send effect, they're both entities.

Currently Skript will send the message to whichever event-value was registered first, or placed in order of subclass. The highest subclass is always first (Skript is usually smart enough to search with converters and get the correct one just not when there is two of same type), so this will pick the egg. This is why Skript has excluded events for the event-value register method, to manually explain per event-value.

This pull request will do that automatically, as we cannot always manually adjust the error or determine when and where they collide. Also addons.

So for my example above, this will be the following error:

Notes:

• For context if you don't know, in the EffMessage a default expression would be the [%commandsenders%] and this means that the user doesn't need to define the command senders, it'll select from the event-values or any other default expression present. Example: on player join: -> send "Hello!"
• Unfortunately I had to modify the main event-value getter collection method to be a List return so that we can properly calculate the possible getters. Makes it look harder to understand, but it's what's needed.
• I changed the command sender noun type name to command sender¦s rather than player¦s/console as a command sender can now be an entity and this avoids a confusing line for EffMessage (The most likely origin of this error).
• I believe this is a better solution than Event value priority #4858
• I also disallowed exact duplicate event-value registering, we don't need an addon registering an already present exact event-value. This can be problematic which was an original issue in Event value priority #4858

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Target Minecraft Versions: any
Requirements: none
Related Issues: #4787

[TheLimeGlass]

This pull request just helped me solve a Skript user's issue where

on entity target:
    if entity's name is "&6Corrupted Golem":
        if target is not player:
            cancel event

Was not working and the user didn't know why. The reasoning was because target could have been player's target or the entities target and also player is an assumption so a would be needed to describe the type of the target. Solution code would be:

on entity target:
    if entity's name is "&6Corrupted Golem":
        if target of event-entity is not a player:
            cancel event

Crazy how I luckily still had this pull request on my current branch as I tested their code to help them out.
Forced me to properly understand what Skript was reading and understand the problem with the new given error.

[sovdeeth]

nice pr!