NEW resolve linkable requirement

[muskie9]

As of now sheadawson/silverstripe-linkable is shown as unsupported. Determining if this is something we should pull what's used into this module, find an alternative, or figure something else out will need to happen before we get too much further with updates to this element.

[NightJar]

As of now (5 years later, lol) linkable is still unsupported, but Shea does merge the occasional PR to keep it functional.
It is a bit late for this module as a refactor (fcca8ee) has already taken place (twice) to use Gorrie Coe's Silverstripe Embed module instead.

But in a cruel twist of events, Gorrie will never maintain nor merge any future PR to keep functionality (RIP 🪦).

DNA have forked embed, but maintenance does not appear to be a forefocus - I imagine doing only what is necessary to keep the module usable in their client projects (a common tale, even with my own modules).

I guess the question from here is:
Should this module go back to linkable, or pick up a fork with dubious maintenance to continue with embed?
OR remove the depenencies and consume embed/embed directly instead (upstream library of both module options)?

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If the refactor and CMS upgrade stays, it should at least be tagged 3.0.0 (because breaking change). I can probably look at contributing a migration script if this is the case.