BlockSwitcher: Add README and JS doc for BlockSwitcher component

[SainathPoojary]

related to: #22891

What?

This PR adds documentation for the BlockSwitcher component, including JSDoc comments and an updated README with usage examples and prop details.

Why?

The goal of this PR is to improve the documentation for the BlockSwitcher component, making it easier for developers to understand how to use it. The updates help clarify the component’s purpose and usage.

How?

The JSDoc comments within the code have been updated, and the README now includes examples and explanations for the BlockSwitcher component and its clientIds prop.

[github-actions]

Warning: Type of PR label mismatch

To merge this PR, it requires exactly 1 label indicating the type of PR. Other labels are optional and not being checked here.

• Type-related labels to choose from: [Type] Automated Testing, [Type] Breaking Change, [Type] Bug, [Type] Build Tooling, [Type] Code Quality, [Type] Copy, [Type] Developer Documentation, [Type] Enhancement, [Type] Experimental, [Type] Feature, [Type] New API, [Type] Task, [Type] Technical Prototype, [Type] Performance, [Type] Project Management, [Type] Regression, [Type] Security, [Type] WP Core Ticket, Backport from WordPress Core, Gutenberg Plugin.
• Labels found: .

Read more about Type labels in Gutenberg. Don't worry if you don't have the required permissions to add labels; the PR reviewer should be able to help with the task.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: SainathPoojary <[email protected]>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.