Enhancement: prevent serialized data by default

[glaubersilva]

Resolves GIVE-1294

Description

This PR implements a few improvements and unit tests for our Utils functions related to serialized data.

This PR also changes the give_clean() function to unserialize all data input by default, but it is possible to allow serialized data by setting the $allow_serialized_data to true.

Last, but not least important, this PR also adds a new migration to unserialize data from the _give_donor_billing_title_prefix donation meta value.

Affects

As many places are using the give_clean() method, these changes affect the entire codebase, but especially the submission of new donations for v2 forms.

Testing Instructions

1. Run the composer test -- --filter UtilsTest command in your terminal.
2. Manually submit a few donations using v2 forms.

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Reviewed by the designer (if follows a design)
• Self Review of code and UX completed

[jonwaldstein]

@glaubersilva awesome job, thanks for doing this! (just added a few notes)

[rickalday]

Passed manual QA tests.