Add support for Label components

[mkrasnitski]

Labels are a new top-level component only supported in modals that can hold a Text Input or Select Menu inside it. Oddly enough, the label and description are removed from the label payload when sent back as part of a modal response. See the docs.

Text Inputs inside Action Rows are deprecated, therefore I removed the InputText variant for ActionRowComponent. Also, at the moment modals can include Action Rows, Text Displays, and Labels as top-level components, so I changed modal responses to store Component instead of ActionRow and added a text method to quick modals. I thought about adding select menu support to quick modals but the methods felt a little too verbose.

[GnomedDev]

Why remove StaticU8? I'm fine with it, as it's a minor performance opt, but I just want the reason written down somewhere.

[mkrasnitski]

The CreateButton and CreateInputText structs have a kind field of type ComponentType already, so this is an inconsistency that I wanted to resolve. Also, ComponentType is a fake enum since it uses the enum_number! macro, meaning it's actually a newtype around u8, same as StaticU8. I'll make a follow-up PR removing the kind fields entirely and just inserting it at serialization time, since it doesn't serve any other purpose.

[DPlayer234]

Wasn't that the point of StaticU8? It was a ZST that would serialize an integer but not take up any memory at runtime.