[Debugger Visualizers] Unify *-gnu and *-msvc enum output

[Walnut356]

Followup patch to #145218

Ports the msvc enum synthetic/summary logic to the gnu handlers so they have identical output. Also removes the "look-through-pointers" logic that caused #147450

I know we don't run the test suite in CI anymore, but it's still useful locally so I updated the relevant tests.

[rustbot]

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[rustbot]

This PR was rebased onto a different master commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[Mark-Simulacrum]

@bors r+

[bors]

📌 Commit d8b5ad9 has been approved by Mark-Simulacrum

It is now in the queue for this repository.

[matthiaskrgr]

@bors rollup=iffy

[bors]

☔ The latest upstream changes (presumably #148721) made this pull request unmergeable. Please resolve the merge conflicts.