Add PascalCase slug to create-block template strings

[opr]

Description

This PR will make a new token available to the templated files used with @wordpress/create-block. It will allow templates to replace {{slugPascalCase}} with the extension's slug but in PascalCase.

This could be useful in cases where templates generate classes, These should be written in PascalCase, and currently there's no way to do this.

How has this been tested?

I have created an example template package, (https://www.npmjs.com/package/blocks-template) the repo for this package is here: https://github.com/opr/blocks-template/ and the slugPascalCase is used in the $slug.php.mustache file.

From the root of this repo:

1. Run npx wp-create-block -t blocks-template my-test-extension.
2. Navigate to my-test-extension and view my-test-extension.php
3. See the class name generated is MyTestExtension_Blocks_Integration

Types of changes

New feature to the create-block package.

Checklist:

• My code is [manually] tested.
• My code follows the WordPress code style.

[github-actions]

👋 Thanks for your first Pull Request and for helping build the future of Gutenberg and WordPress, @opr! In case you missed it, we'd love to have you join us in our Slack community, where we hold regularly weekly meetings open to anyone to coordinate with each other.

If you want to learn more about WordPress development in general, check out the Core Handbook full of helpful information.

[opr]

I'm not sure if I'll need to update the changelog and package versions in this PR, or if this will be done as a next step when releasing the package. If it's required now then please let me know and I'll add it :)

[mkaz]

This looks good, thank you for the contribution.

Yes, you do need to update the CHANGELOG under the ## Unreleased section. Since it looks like there is not anything added yet. Add a subsection ### New Features and your update.

You do not need to update version numbers, that is handled by the release process.

[mkaz]

Thanks for the update, I made a minor change to use the precise name for the variable.

[opr]

Thanks for the update, I made a minor change to use the precise name for the variable.

Thanks for the review and thanks for updating that, I appreciate it.

[github-actions]

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