Add support for modifying settings values using RegEx

[ancientcatz]

Issue Checklist

• I confirm that this feature request has not been previously suggested.
• I agree to follow the project's code of conduct.
• I have checked and verified that I am using the latest version of Geto from GitHub or F-Droid.

Additional terms

• I understand that feature requests are subject to evaluation and may not be implemented immediately.
• I agree to provide additional details if needed for a clearer understanding of the requested feature.

Feature description

It would be helpful if settings values could be modified using regular expressions (RegEx) rather than full-value replacements. This would allow specific parts of a setting to be added or removed without replacing the entire value.

Use Case

Currently, when enabling accessibility services (or similar settings), the app replaces the entire value. This causes issues, as it overwrites any existing settings rather than appending to them. With RegEx support, we could match and modify only specific parts of the value. For example, adding an accessibility service would append it to the existing list, and reverting could remove just that service without touching the rest of the settings.

Benefits

• Preserves original settings by avoiding full-value replacements.

• Enables selective modifications, making the app more flexible and reliable.

• Reduces the risk of unintended side effects from overwriting settings values, improving compatibility and stability.