feat(tree): Support long forms for --format variables

[epage]

What does this PR try to resolve?

This came out of #16192 (comment)

How to test and review this PR?

As for testing, I was unsure if it was worth exhaustively testing every variant of every format option

[rustbot]

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[epage]

@rfcbot fcp merge

This proposes adding to cargo tree --format long forms of each one-letter variable

• {f}: {features}
• {p}: {package}
• {l}: {license}
• {r}: {repository}

This moves us away from the precedent that everything is short to short forms are a convenience for commonly used items.

[rust-rfcbot]

Team member @epage has proposed to merge this. The next step is review by the rest of the tagged team members:

• @0xPoe
• @Eh2406
• @Muscraft
• @arlosi
• @ehuss
• @epage
• @joshtriplett
• @weihanglo

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

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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.