Document and update Cauldron behaviors / utils

We have a few Cauldron utilities that are undocumented but exported:

https://github.com/dequelabs/cauldron/blob/d6bcd11e229c932b4b456afc995c34ebbd76f5e9/packages/react/src/index.ts#L141-L143

Since these are part of our public api, we cannot significantly modify these exported utils without potentially causing breaking changes. We should properly document any "behaviors" we want to include as a part of Cauldron as well as set the expected usage of these utilities. This will require a proposal that should include:

- How these behaviors should be written (hooks vs non-hooks)
- When a function should be written as a behavior
- How these behaviors should be exported from Cauldron

It may be expected that removing some of these existing utilities that may not need to be exported may result in breaking changes and should be included in the proposal on how we will minimize the risk.

Start with packages/react/src/index.ts at lines 141–143 to identify the exported Cauldron utilities and their current public API. Prepare a proposal covering hooks versus non-hooks, when to use a behavior, how behaviors should be exported, and how to minimize breaking-change risk if utilities are removed; done means the proposal documents expected usage and the requested decisions.

Written by the indexing model from the issue text.