Support modifying the Roblox reflection database

[hoontee]

Problem

When Roblox adds new properties and Enums, Lune requires an update for them to become accessible.

Solution

Implement functions for adding new Enums, Enum values, Classes, and Class properties.

These should affect serialization.

-- Add a new Enum.
Database:AddEnum(name: string, {[string]: number}): DatabaseEnum

-- Add a new Enum value.
DatabaseEnum:SetValue(name: string, value: number)

-- Add a new Class.
Database:AddClass(name: string, {[string]: {ValueType: any, Default: any}}): DatabaseClass

-- Add a new Class property.
DatabaseClass:SetProperty(property: string, valueType: any, default: any)