[rustdoc] issues of the three-big-buttons

[liigo]

PR #129545 introduced a new style for rustdoc API pages.

I appreciate the author's efforts. But the new style still has a few shortcomings.

• It's not as compact as the old style, more than one line space in vertical is wasted.
• It does not utilize the horizontal space on search-box's right. (Are we really need a so big search box? as nearly wide as screen?)
• The icon+text button is unnecessary, there's well known icons for help/setting/folding, no text is needed here.
• The three-big-buttons may attract user's attention, and distract exploring contents.
• The top-right version+source are moved to top-left, while leaving most other version+sources at right, that makes a big UX pain.

That PR said:

The settings, help, and summary buttons are also too hard to recognize.

I don't think that's right. Gear-icon for setting, question-mark-icon for help, +/--icon for folding, are widely used all over the world, the meaning is clear. The top-right position of the window is also easy to find and reach. The search box has a tip of '? for more options' in its placehold, you may type ‘?’ key to 'click' the help button. There's document in help page to help you find folding button. That's enough, for those low utilization rate buttons. Folding (aka summary) button's icon may use a different color to improve recogniztion.

That PR made those buttons very big, bigger than any other items of the page. That's an UX issue too (as i said above).

I propose:

• Make the three-big-buttons smaller, by removing text (and add tooltips), and move them to right of search-box.
• Move top-left version+source back to top-right (below the new three-icon-buttons).
• Change color of folding-button's icon to improve its recogniztion.
• Change order of the new three-icon-buttons: help, setting, folding.
• Improve help page: to match collapse/expand vs summary/show-all vs folding/unfolding.

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links: new style, old style

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[Urgau]

cc @notriddle @GuillaumeGomez

[notriddle]

The settings, help, and summary buttons are also too hard to recognize.

I don't think that's right.

But the PR links to the first- and second-hand reports of several people who didn't recognize them. Here they are again, with quotes extracted from the text this time.

• "It's hard to see the settings icon, it seems to be a part of the search bar.". This has nothing to do with the icon being recognized, but the placement and styling misled the user about its scope of effect.
• "I've talked to 3+ experienced rust developers this morning, all of whom were unaware of the existence of the help popup."
• "The collapse all button does work really nicely - but I didn't even know what it was until I read this issue."
• "Amazing! [The collapse all button] will save me a lot of time. It's not very clear though that it collapses the whole page. I would have never known without you pointing that out"

[notriddle]

Fixed by #144476

[liigo]

Now there're four big buttons.