Modular Reflection

## Goal Description

The `bevy_reflect` crate has a lot of related, yet distinct features. Not all features are needed for every use case and their forced inclusion can slow compile times and increase binary sizes unnecessarily. A consumer of `bevy_reflect` should have more say in what features are included and what code gets generated per their specific needs.

## Goal Status

This is a potential [Bevy Project Goal](https://bevy.org/learn/contribute/project-information/project-goals/). Its state on the [Project Goals Board](https://github.com/orgs/bevyengine/projects/23/views/1) determines if it is Proposed, Postponed, Blocked (Approved), Inactive (Approved), Active (Approved), Completed, or Declined.

- **Staffing SMEs**: @MrGVSV
- **Working Group Link**: [link](https://discord.com/channels/691052431525675048/1525601380482683041)
- **Design Documents**: Design documents not yet written