Backport 1.12.2 config subcategory behavior

[Lyfts]

In 1.12.2 you can declare static instances of inner classes in your @Config annotated class, those instances will then be automatically treated and parsed as subcategories of that class.

There's an example of it here https://github.com/GTNewHorizons/GTNHLib/blob/056959f0f51e3f2699274d264a9a7887a257f315/src/main/java/com/gtnewhorizon/gtnhlib/config/TestConfig.java

This will automagically be parsed into

# Configuration file

test {
    # This is a test boolean [default: true]
    B:testBoolean=true

    # This is a test double [range: 4.9E-324 ~ 1.7976931348623157E308, default: 1.0]
    D:testDouble=1.0

    # This is a test enum
    # Possible values: [TEST1, TEST2, TEST3]
    #  [default: TEST1]
    S:testEnum=TEST1

    # This is a test int [range: -2147483648 ~ 2147483647, default: 1]
    I:testInt=1

    ##########################################################################################################
    # subconfig
    #--------------------------------------------------------------------------------------------------------#
    # This is a sub config
    ##########################################################################################################

    subconfig {
        # This is a test boolean [default: true]
        B:testBoolean=true

        # This is a test double [range: 4.9E-324 ~ 1.7976931348623157E308, default: 1.0]
        D:testDouble=1.0

        # This is a test enum
        # Possible values: [TEST1, TEST2, TEST3]
        #  [default: TEST1]
        S:testEnum=TEST1

        # This is a test int [range: -2147483648 ~ 2147483647, default: 1]
        I:testInt=1

        ##########################################################################################################
        # doublesubconfig
        #--------------------------------------------------------------------------------------------------------#
        # This is a nested sub config
        ##########################################################################################################

        doublesubconfig {
            # This is a test boolean [default: true]
            B:testBoolean=true

            # This is a test double [range: 4.9E-324 ~ 1.7976931348623157E308, default: 1.0]
            D:testDouble=1.0

            # This is a test enum
            # Possible values: [TEST1, TEST2, TEST3]
            #  [default: TEST1]
            S:testEnum=TEST1

            # This is a test int [range: -2147483648 ~ 2147483647, default: 1]
            I:testInt=1
        }

    }

}

I also made it possible to get categorized IConfigElements for the config gui so that it will look like this

As opposed to something like Hodgepodge's current config gui where all the elements are on one page with a humongous scrollbar.

Also adds a method to save the current field values to the config file & adds double as a config option, because why tf is double[] an option while double isn't

[Caedis]

Think its time to refactor processConfigInternal

Maybe add a method to the annotations so they the logic is there and we just pass it whatever it needs

If thats possible