Improve ::generateSampleValue() for common field types

At the moment this is tackling things in one patch rather than sub-issues, so moving to a task. If we want to split out we can do that later.

New functions will have to be typehinted
Schema additions will need a post_update hook (with test case)

I'm looking into customizing generated dummy content using devel_generate. That uses the fields generateSampleValue() function.

The two places I'm aware of this function being used are for in the Layout Builder UI and Devel Generate.

In LB, I want to see dummy values that resemble my content.

In Devel Generate, I want dummy values in line with the data I'm using.

To override this function on a field... I have to create my own class and override the field?

What I'm looking for is an easier way to override generateSampleValue().

@catch and @smustgrave Issue category changed from Plan to Task, and the issue status is "Needs work", but what exactly the proposed solution?

If somebody wants to work on this, then where to start and a „how to implement” guide would be useful.
For me the hints from comment #29 is not enough.

New functions will have to be typehinted
Schema additions will need a post_update hook (with test case)

The Needs Review Queue Bot → tested this issue.

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