Generic character mapping MiniMessage tag (for small caps)

[kezz]

One of our most common requests in the discord support channels is for tags that can convert text into sᴍᴀʟʟ ᴄᴀᴘs, a pretty common set of characters used in Minecraft servers. As Modifying tags are relatively complicated compared to normal tags, we should provide a utility method to create a Modifying tag that simply maps characters or groups of characters into other characters. This could also have other use cases beyond just a small caps tag.