Make the table of incompatible releases in UpdateManagerUpdateForm more theme-friendly

Problem/Motivation

Follow-up to address #3113992-85: The 'Update' page has no idea that some updates are incompatible → .
In that issue, we add a new table to the UpdateManagerUpdateForm (that powers the 'Update' page at /admin/reports/updates/update) for "Incompatible releases". It includes the info about the range of versions of core that each incompatible release requires in a classless <div>. As @xjm eloquently wrote:

Why're we sticking it in a classless child div? Some divitis up in here.

;) I was being pragmatic trying to fix a critical bug with minimal changes, but we all agree this isn't ideal.

Proposed resolution

Make this table more theme-friendly.
E.g. add a new Twig template for that table, or perhaps for rows in that table, or something.

Remaining tasks

Decide what to do.
Implement it and remove @todo pointing here.
Reviews.
RTBC.
Commit.

User interface changes

Hopefully none, other than the ability to more easily modify this UI.

API changes

Probably a new Twig template, although I don't think that's considered API.

Data model changes

None.

Release notes snippet

TBD.