- Closes#18868
## Summary
This PR introduces a new slash command `/selection` to enhance the
usability of the assistant's quote selection feature.
## Changes Made
1. Extracted a function from the `assistant: quote selection` action to
find the selected text and format it as an assistant section.
2. Created a new slash command `/selection` that utilizes the extracted
function to achieve the same effect as the existing `assistant: quote
selection` action.
3. Updated the documentation to include information about the new
`/selection` slash command.
Release Notes:
- Moved the text selection action to a slash command (`/selection`) in
the assistant panel
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Co-authored-by: Danilo Leal <67129314+danilo-leal@users.noreply.github.com>
Co-authored-by: Bennet Bo Fenner <bennet@zed.dev>
