Deprecation notice in rocketship_blocks_title_preprocess_block

Problem/Motivation

The Rocketship Blocks module is using the deprecated PHP substr() function with a potential null parameter in rocketship_blocks_title_preprocess_block(). This generates deprecation notices in PHP 8.1+ and could lead to runtime errors in future PHP versions. The issue needs to be addressed to ensure compatibility with newer PHP versions and maintain code quality.

Steps to reproduce

1. Install the Rocketship Core module and enable Rocketship Blocks submodule
2. Enable deprecation notices in your PHP configuration
3. Navigate to a page where rocketship_blocks_title_preprocess_block() is called
4. Check the logs or screen for the deprecation notice:
   

   Deprecated function: substr(): Passing null to parameter #1 ($string) of type string is deprecated in rocketship_blocks_title_preprocess_block() (line 229 of modules/contrib/rocketship_core/modules/rocketship_blocks/rocketship_blocks.module)

Proposed resolution

Replace the deprecated substr() function with str_starts_with(), which is more appropriate for prefix checking and handles null values better. This function was introduced in PHP 8.0 and is the recommended way to check string prefixes.

Remaining tasks

1. Create a patch replacing substr() with str_starts_with()
2. Add appropriate null checking if necessary
3. Test the changes to ensure functionality remains the same
4. Update module documentation if needed

User interface changes

None. This is a code-level change that doesn't affect the user interface.

API changes

None. This is an internal function modification that doesn't affect the module's API.

Data model changes

None. This change only affects code functionality and doesn't modify any data structures or storage.