Core: Deprecate/Remove FilterModes is, isNot, before, after

[melloware]

Based on conversation in: primefaces/primelocale#143

OK I looked at the source code and those 4 are not in any other lib PrimeFaces, PrimeVue or PrimeReact.

It seems they are just shortcuts to the real methods.

        is: (value: any, filter: any, filterLocale?: any): boolean => {
            return this.filters.equals(value, filter, filterLocale);
        },

        isNot: (value: any, filter: any, filterLocale?: any): boolean => {
            return this.filters.notEquals(value, filter, filterLocale);
        },

        before: (value: any, filter: any, filterLocale?: any): boolean => {
            return this.filters.lt(value, filter, filterLocale);
        },

        after: (value: any, filter: any, filterLocale?: any): boolean => {
            return this.filters.gt(value, filter, filterLocale);
        },

So I actually think these 4 are deprecated in PrimeNG and replaced with the 4 values that have translations so somewhere along the lines PrimeTek made all the libraries in line and left these 4 for backwards compatibility but they should probably be marked deprecated.